I just bought a basic, c5 I believe, sleep number, and so far its really good. I too have several bad discs in my lower back. I find memory foam HOT and I cannot deal with it. My last mattress was very firm, but had a pillow top. Horrible. I woke every morning in serious pain. The pillow-top was hot and gave zero support. Most of the time I ended up sleeping on the floor to get out of pain. I've not had to do that yet.
Too expensive, and too much hype, for sure. The thing is built very well. Actually, the price is more easy to understand after seeing the pieces of the matress fit together..