On a recent trip I became incredible hulk-angry at the state of our (original to the rig) mattress. I was done with feeling the not-so-gentle caress of every single coil spring and waking up every morning feeling like my hips were dislocated.
The campground we were at (which is a huge, sprawling place with a big seasonal population) actually had just opened a "furniture" store for the seasonal residents and they actually had RV-sized mattresses. This was advertised in the packet we got when we pulled in, but i hadn't read it. The wife, fortunately, had. I Couldn't get down to that store fast enough. That night I slept better (in the camper) than I maybe ever had!