We replaced the nasty mattress that was in our TT with a Spa Sensations, 8-inch gel memory foam mattress from Walmart. It slept as good, if not better than our Tempurpedic we had in our house. When we sold that TT, we ordered a new mattress to go into our fifth wheel before we even took possession of it. When our Tempurpedic finally bit the dust at home, we replaced it with a 10-inch SS mattress. It's been good for about 6 years.
I guess it is just according to how much work, money and time you want to put into a 20 year old camper. Right now, it's not worth much, maybe 1-2K, but that might be stretching a bit with a soft floor.