Knit Picks and Knitter’s Pride both have sets that are ~$50 on Amazon. Buying the set is the most cost-efficient way to purchase interchangeable needles. If you don’t feel strongly one way or the other about supporting your LYS on this (I feel ok compromising here because I support my LYS with my consistent yarn purchases), just order from amazon whatever you can’t try in-store and return them if you don’t like them. Karbonz and Royales are quite expensive. These are great and affordable and are the short set, perfect for your hat making. I don’t own that set personally but I have the regular-length set in blonde wood from them. I also own a set of the Dreamz and the Nova Platina from Knitter’s Pride. The Knit Picks short needles are a somewhat newer offering from them, which is the only reason I don’t own them. I purchased my short needles from Knitter’s Pride several years ago and just haven’t been able to justify spending more money on needles with my husband yet.

Now the needles I linked are great needles and very affordable. But! The Karbonz and Royales are pretty expensive and can go up to $150 or higher for gift sets. Even the set with just the needles is around $90-100. If I were you, I’d totally get them because I have no impulse control lol but they aren’t strictly necessary. Plus, you might not know how to appreciate them yet if you purchase them right away, and end up not loving them because you feel they weren’t worth the money. Realistically, the Dreamz or the short Caspian set would be a great fit for you. I enjoy the Knit Picks a little more so I’d recommend the Caspian, but the main difference is aesthetic rather than utility.

Fixed circulars are exactly that—fixed. You can’t really use them for many projects so you could end up spending more money in the long run buying needles that you only use a few times because their length is wrong or their size is wrong. If you need a size 4 16 in and all you have is a size 6 16 in, you’ll have to go out to the store. With interchangeables, you’ll never have that problem. The only downside is that needles small enough for socks aren’t usually produced for interchangeables. You’ll either have to buy fixed circulars or stay with dpns. Most interchangeable sets only go as small as size 4 but socks typically need size 1 or 2.