I had to buy a mattress last year and did a pretty deep dive into the world of mattresses. What I learned is that there's no meaningful research on what's "best", and sleep experts say that it's 100% personal preference (and marketing).

So I bought the cheapest thing on amazon with the best reviews in the size that I needed, which was maybe 25% of the price of Casper or Leesa (and those are about half the price of a traditional mattress). It's absolutely fine. If anything, I sleep better knowing that if I destroy it or have to move, I can just throw it out and buy another one.

One note: if you read enough reviews, you'll notice that some budget foam mattresses can have a smell to them. I assume this is the main thing that "premium" foam mattresses have actually addressed, but obviously it's not advertised as "we have the least smelly product!".

It's really as simple as finding a well reviewed hunk of foam, or at least it was for me, as mine arrived odor-free.