I just wanted to share my find on a good mattress for my back. I had back surgery years ago and subsequently annoying back muscle spasms at night, which I believe were worsened by my too soft, pillow-top mattress. (mattress was ok for the first two years, but then started to sag)
I have purchased a new mattress that I think has really made a difference. I found a firm silver King Koil from Sleepy's, which I was able to negotiate to half of the price (about $500, mattress only). I know there are comparable brands, but make sure it is firm and well constructed like this one.
Then I added soft padding to the top - an egg foam memory mattress topper from Bed, Bath (this was $35), and a Charter Club visco pad ($100 on sale) and thick cotton mattress pad from Macy's (this was about $50 I think). I know. Sounds excessive but I am seriously happy.
I think this solution is the best - I have good support but a soft top. And unlike the attached pillow top, I can replace the foam memory crates in a few years without buying a whole new mattress.
I hope this helps! I looked a lot through these forums to help me figure out a good solution, and I know mattress buying can be incredibly stressful.... you feel like you are being scammed the whole time. so good luck!