I put a household queen size Serta Perfect Sleeper pillow top mattress in the master bedroom of my Blue Ridge 3705BH. It was a couple inches longer than the original mattress, making it come right up against the dresser when the slide is pulled in. If it had been even an inch longer, it wouldn't have worked, so it would pay to measure before you buy. I had this one on hand anyway and it fit, so win-win for me. The mattress that came in it was supposedly a pillow-top, but it left a lot to be desired.
Mike in Tennessee
Former 2 time FR owner
2007 Crossroads Cruiser 30QB Fifth Wheel
2008 F-250 Lariat 4x4 6.4 Powerstroke
Firestone Ride-Rites w/cab control