I did a lot of research while I was looking, and it's hard to really know what to believe. I'll try to summarize what I learned but unfortunately even having bought a mattress that seems good so far, it's still hard to tell if I made a good decision or not.

Comfort is subjective. If a bed feels good to you and doesn't cause you pain from sleeping in it then it's good in that regard. Unfortunately with online mattresses there's no way to test before you buy, and personally I don't think that lying on a bed for a few minutes in a store is really going to tell you that much either (or at least, it wouldn't for me). I feel like this is always a bit of a dice roll, so just make sure there's a good return policy and try to get something you think you will like.

As for durability, apparently if the bed has foam it's more likely to last if it's higher density. You can read some detail about that here. I have also read that latex mattresses are the most durable foam mattresses, and also that coils are pretty durable. This is just what I read, so take it with a grain of salt.

Personally I went with a Brooklyn Bedding Signature. It's comfortable, but I'll have to see how it holds up over the long run. I can't really make a recommendation but so far so good. I know the foams are high density for polyfoam. I can't really make a recommendation but so far so good. Another one I would be interested in if I were to choose again is the Nest Bedding Latex Hybrid.