If you want something that will lay really flat, the Kenmore canisters such as the 400 Series that your cleaner owns would work fine. People like those Kenmore canisters because they are versatile for how cheap they are, cheap enough to where you do not feel too bad about beating the heck out of one, and they clean well. As long as you do not mind dragging a canister, you would like the features of one. I am not sure how easy your house cleaner made using their unit look, but although there is a bit of a learning curve, you get used to it eventually. If you have used a canister, disregard that little tangent.
Something such as this Kenmore 200 Series would be your best bet for getting under small spaces because it comes with the classic two-piece wand that allows you to turn the handle a full 90 degrees instead of the extender wand that comes with models such as this one, although the extender wand versions still lay pretty flat compared to any upright. Pretty much any Kenmore canister would be fine, as they all have similar strong points and similar issues.
The differences between the 200 Series and the 400 Series are that the 400 Series has the power slider on the handle instead of in the form of a button on the canister, a variable motor speed control on the handle, and a bag check indicator. As far as the colors of the 200 and 400 Series models go, the main differences are the attachments and wands, so pay attention to that. Other than that, the units are the same.
There are also models such as the 600, 700, and 800 Series that come with longer hoses, more attachment, more features, and what not if you are curious about those, although the 200 and 400 Series models are a stellar deal and can fit extra attachments such as this miniature power nozzle, dedicated upholstery tool, dedicated dusting brush, and onward.
I hope that description was a little more helpful than linking long-winded videos that do not directly address your specific situation. Miele makes wonderful canisters, but to get one with a power nozzle, you have to pay around double your maximum budget, hence why we suggest the basic Kenmore canisters, which clean well and are fine machines, but obviously are not to the level of durability and user-friendliness of a Miele or SEBO canister.
The Hoover uprights are fine, but they are a little more work to get to lay underneath something such as a bed, their hard floor performance will not blow you away due to the lack of a specialized attachment or head for them, they lack sealed HEPA exhaust filtration, and the build quality is a little worse than the Kenmores. I know a lot of people love the Hoover T-Series bagged (formerly Tempo) and I actually like them as well, but Hoover discontinued them and the price has inflated to $200, being more than I think the units are worth. They were a spectacular deal when you could get one for $99 and even up to $150, but unfortunately those days have passed. They do have nice bags and the machines are lightweight, though, so I would not totally discount one if you are considering a bagged upright.
The Orecks, aside from being relatively expensive for what type of canister they are, would not be great for the carpet that you have. They are not terrible vacuum cleaners and have their purpose for sure, but the Buster is not something I think you would like based on your needs.
The Bissell 3059 is not as bad as it could be, but also not totally worth that price, in my opinion. The manufacturer for that particular Bissell model, Eup of China, makes relatively decent budget machines and the CleanView Lift-Off models are fine and quite a bit better than most of what Bissell offers, but you listed better vacuum cleaners within your options and it would not be my first choice.
The Hoover T-Series bagged is a decent vacuum cleaner. A lot of folks on here love them. I am fairly neutral on them. They clean well and are "no nonsense" in how simple they are. The model, according to Hoover, is technically discontinued, so the price has inflated quite a bit. They used to be sold for as low as $99, but regularly sat at around $130 or so. To me, they were a better deal at that price since the build quality is not great on them and things such as the attachment clips often break through normal use. Still, they work well, are pretty user-friendly, and are lightweight.
The Hoover WindTunnel 3 Max Performance Pet is a model and its variants that I used to recommend for somebody who wants a cheap upright bagless vacuum cleaner, but Hoover has substantially cut back on the features and build quality to the point where it is practically a different vacuum cleaner than when they first released it. Despite it being pictured in the listing with a belt tensioner that would allow it to have the brush roll turned off for use on hard floors, it no longer arrives with that feature. Also, it used to come with a changeover that provided a more direct air path to the head, giving it extra power, but they removed that too and I can see that they bothered to remove it from the pictures in the listing, but I can see where they just blacked it out on the left side of the units in the pictures. They also reduced the quality of plastic. I had one and it was so flimsy that I could grab the top of the handle, twist it, and the bin would pop off the unit just by that. This is definitely the worst vacuum cleaner you listed and Hoover should just discontinue it.
The Hoover MAXLife Swivel UH75210 is quite different than the WindTunnel 3, being a fresh design that trimmed much of the fat of the WindTunnel 3 and is better about being cheap. There is not much I have to say about the MAXLife. They clean alright and are priced right. The build quality is nothing spectacular, but the price reflects that and it at least stays together in one piece. One thing worth mentioning is that they take stretch belts that need to be replaced every so often and there is also no way to stop the brush roll. Nonetheless, since you seem to not have any delicate flooring, the spinning brush should not hurt them.
The Kenmore Elite 21814 is a solid budget option when it goes on sale, but I would not go for it in your situation unless you really think you need all those extra features. I typically recommend the fancy Kenmore canisters if somebody wants to have some of the features of a premium canister, but is on a budget that cannot stretch beyond a certain point. Kenmore even sells cheaper canisters ranging from the 200 Series to the 600 Series bagless and so forth that would likely be in a more comfortable price range. The Kenmore canisters are not bad machines. They are a step above the Hoovers in build quality and also some of the only power nozzle canister options for folks on a budget in the United States.
The Kenmore CrossOver DU3017 is my go-to suggestion for a bagless upright. I personally think it is the best budget machine on this list because it provides attractive features such as a lifetime belt, brush roll shutoff with a separate brush roll motor, a lift-away mode, a quick-draw wand, a multi-cyclonic bin with a washable cloth pre-motor filter, sealed exhaust filtration, and so forth. Kenmore does sell some garbage bagless uprights that look similar to the CrossOver, but the CrossOver is different because it was designed by Panasonic and is made in their own factory unlike some of the cheaper bagless uprights that I do not recommend. The build quality is significantly better than the Hoovers and Bissell too.
Out of all the units you listed, I would pick the CrossOver DU3017 or the WindTunnel T-Series UH30310. The WindTunnel is nice if you want a bagged and lightweight unit that is simple and easy to maintain and the CrossOver is nice if you want a competently designed bagless machine with a bunch of extra features that is more versatile in attachment mode. Between the two, the quality of the CrossOver is a whole lot better, which is what sways me towards the CrossOver, but you may like the simple design or cheaper price of the WindTunnel. Either would do the job, though. Both have brush roll shutoffs for hard floors, some kind of HEPA filtration whether it is HEPA bags or a HEPA exhaust filter, a couple basic attachments, and so forth.