I have had one of these for over 5 years now and its going strong. it's got an internal frame, so the back support is really good. It can get pretty roomy, or you can cinch it down so it's a lot slimmer. It's a top loader with a big main pocket, which I find is great for pulling out books and stuff, but not as good for organization or if you need to keep things at the bottom. I have an EDC-esc pouch that I keep all my cables and knick-knacks in, so it isn't a huge deal for me.

https://www.amazon.com/Kelty-Unisexs-Redtail-Hiking-Backpack/dp/B078XXSSRL

(search around, it's kind of an older model. I think you could find a better price)