I like supportive beds rather than soft beds or water beds. When I moved to my last apartment I needed a new bed and I didn't want to pay to much. Although you can end up spending a lot on a Sleep Number, I bought mine for just over a thousand.
I didn't buy it for back pain or anything in particular. I just needed a new bed and wanted something a bit more modern than the usual spring mattress. I'd heard that purely foam mattresses can get really hot and eventually get dips from the foam not bouncing back to its original shape. Therefore, I looked into Select Comfort beds instead. I went to a store and tried it out there. You can't really take a nap at the store, so it doesn't really give you a good feel as to what the bed can do.
The bed can help with back pain in that it doesn't cause any. I've woken up with major back aches with water beds and some minor aches occasionally with a spring mattress. This isn't the case with my Sleep Number. I've a lower end, Queen size Sleep Number. My number is typically 70. 70 is high enough to support me well, but low enough to form to my back. Due to the chamber design, the bed will support your lumbar, which is crucial.