Well after much procrastination, the prospect of visiting relatives finally pushed us to make a decision on a new mattress. Mostly based on a Consumer Reports rating, we settled on trying a memory-foam style: the "Novaform® 14" Primafina Queen Gel" from Costco. We also got the "Sleep Science Queen Folding Mattress Foundation" as a base.
After one night, my wife has declared a success based on how her back felt this morning. No heat issues, which was one of our major concerns with memory-foam. We'll see how it holds up over time...