Tried the futon & foam topper thing..didn't work for me. I've been using queen-sized air mattresses for years and they work fine..very comfortable and packs away if needed. The one I have now is a $17 intex-brand. This summer will be its 4th or 5th season. Eventually it'll pop a leak..and I'll get another, but they can last if you take care of them. The mattress may need a a few pumps of air over a 3-4 day period. Not a perfect solution, but there are few perfect solutions to any problem...they can work.
The cold-air issue is solved via a "Heavy Duty Reflective Survival Space Blanket" laid on top....mylar facing up.

A dedicated for-real mattress is the nicest, but then you need a dedicated space for it or a lowered-from-the-ceiling setup to get it out of the way..in a CTC at least.