We have a Sleep-number bed, and it is the best thing in the whole world for my back ! It is totally adjustable, so we adjust my husbands side for where he sleeps good, and my side where it is perfect for me. And it is easy to change it up or down, so if you feel like you want it either firmer or softer, you just press the button until it feels right for you.
Sleep number beds are expensive, but I found mine on Craigslist, ad got it from some people that were moving and couldn't take it with them. It doesn't have the lifetime warranty like a new one would have had, but we paid $200 for a queen size bed with everything except the frame (regular bed frame), and have had it about 6 years now, so it was a real bargain.
An added benefit was when we had the tornadoes a couple of years ago , and the roof of our house was blown off in the storm, a regular mattress would have been ruined with all the rain that poured in all day long. The sleep number bed is just air bags in a cover, so we just took it apart, hosed it off, and put it out in the sun to dry, and it was as good as new again.