Investigate natural latex. It's made from rubber trees without any chemicals (unlike the tempurpedic foam), and it's delightful to sleep on. I find that I toss and turn much less, so I wake up more rested. It's not cheap, but it lasts much longer than an innerspring mattress, and I consider it an affordable luxury.
A mattress is so personal! Other than the Sleep Number, which is adjustable, I really think you have to try them out for yourself. My hubby and I rented a house on a vacation with a Tempurpedic and we were so excited, but it just didn't work for us. I get hot when I sleep and the way it sucks you down in makes that worse. He is a stomach sleeper and it hurt his lower back (too squishy).
You really need to go and try some out to find what you like. I think that's best done at a large department store with lots of selection. We tried some incredible hotel-quality mattresses, but they were out of our price range (I think around $2000 for mattress and boxspring!). We ended up going with a best-quality Ikea set after trying out probably 25 mattresses, and it's been great so far.
I like my medium firm Dux bed. They have different types of grades... I also like my hammock, havent adjusted to sleep nights in it yet but working on it :) So i can sleep in forrest during summer after workouts or berry/mushroom gatherings.
I bought a Hastens natural mattress here in the UK. It's worth every bit of the extraordinary price. Perhaps go to their site and order a free DVD of their natural mattresses. That'll give plenty of information.
I have a cheaper, fairly thin (6" or so) king sized IKEA mattress, with a 4" thick memory foam topper and a heat dissipating topper to keep the memory foam on (the topper plus the mattress equal the width of a "normal" mattress). Bed is on a platform so it's fairly firm. Out of every bed I've owned (including high end mattresses) I've had the best sleep of my life on it.
The only problem with the thinner mattress on a hard surface, is that it has to be flipped quite often, so every time I change the sheets (weekly), the mattress gets flipped/spun to keep the support levels consistent. Eventually I guess I'll need to get a new mattress, as this one is about 4 years old.