We changed to a SN bed at our home over 12 years ago. When we bought our current coach (new), the foam mattress was a piece of junk that we discarded and replaced with a SN knockoff on our maiden voyage. We have since replaced the knockoff with a genuine Sleep Number mattress (long story).
My other half makes part of her living out of replacing lousy foam mattresses with a "much better" foam mattress. So, we obviously don't discount good foam mattresses as a viable option. However, on SN's scale of 1-100, Chris has her side set at 35, while I wish mine could be set at 150. Can't do that with a foam mattress.
Before anyone suggests it, forget the "egg crate foam" option.