One small piece of advice to go along with all the great stuff already posted:
A good–if you can’t afford great–mattress is extremely important, and should give you years of comfort in exchange for the big outlay of cash.
But don’t forget the little things that help, too. The add-on bed pad is one…I bought a knock-off version at a local discount store, and it’s working great.
The other additions are even more minor: a) I bought a really top-notch ergonomic pillow, the kind with a fatter roll at the front to fit into the notch between your head and shoulders (i.e. it cradles your neck). You can’t believe the difference in the quality of sleep, and the way you’ll feel when you awaken. b) Don’t forget to either buy a “body pillow” or at least ensure that you’ve got a good, fat pillow tucked between your knees whenever you sleep on your side. It keeps your hips and back aligned properly, and has probably done more for my spinal health than the last five years of chiropractic care (and my chiropractor agrees!).
Whatever you decide, give the above a try. Best bang for the buck by far!!