Not from personal experience but- my sister found a twin XL from Linenspa on Amazon and loves it. So much, she bought a second one and put them together. They're in your price range so might want to hunt around and see if any of the options sound like something you'd be interested in. I got a gel topper from Linenspa and it was too firm for me so I gave it to a friend who still uses it and likes it a lot. So it's a bit of a crapshoot but for the price, could try 'em. More on reddit.com

Honestly i don’t really get why people are scared of amazon mattresses. You can usually get decent discounts and deals, and warranties tend to be pretty solid. The main things to watch out for are a) whether the foam uses fiberglass for fire-retardant purposes, some people hate it because it can poke through if the cover tears, and b) checking the return policy/trial period so you’re not stuck if it’s too soft or firm for you. Other than that, just focus on what you want: memory foam vs innerspring, thickness, firmness, and whether you sleep hot. As for recs, you could look at egohome’s mattresses , they’re medium-firm memory foam and are shipped in a box. Just make sure to let it expand fully and read the product instructions for setup. More on reddit.com

IKEA. More on reddit.com

Be careful that whatever mattress you go with doesn't contain fiberglass. It's pretty common in the US for lower end memory foam mattresses to have it, and it can leak out after normal use even if you don't remove the cover. Found that one out the hard way. More on reddit.com