Hi Dee, I went through this about a year ago. I would not have thought memory foam would work for me, but I kept considering it because I kept running across one statistic: the consumer satisfaction rate for memory foam was consistently higher than for any other type of mattress -- and by wide margin. Weirdly, among the small percentage of people dissatisfied with memory foam, the complaint tended to be that they were either too firm or too soft. So it was hard for me to get a handle on what it would be like. I've always preferred firm, so I hated the idea of sinking into something that wouldn't support me. It also felt risky because I've always been sensitive to heat. I also couldn't afford a Tempurpedic, so it felt especially risky to buy a cheap knockoff online.
But I did, and I've never been so happy with a mattress. When you first lie down it's soft like a marshmallow, but very quickly, as it forms around your body, you feel solid support. (Hence it's both soft and firm.) I got a 12-inch king-sized from a company that got pretty good reviews, but it still came delivered in a box about the size of a mini-fridge. I chose one that had a layer for "pressure relief," figuring that might be good for a fairly big guy like me. (So I don't know what other iterations are like.) It was 300-something dollars, and I think a comparable Tempurpedic would be a couple thousand more. I sometimes notice a slight warmth, but it's definitely no sweaty hothouse like I feared. There's an initial smell, kind of like non-toxic latex paint, but it's not unpleasant, and it fades away within a few days.
Anyway, I know it's a tough decision. But that's my experience, for what it's worth. This is the one I got: