Years back we bought a replacement mattress for our 5'er. It was a short queen. The brand was Richardson, made by Serta. Very nice mattress, better than home. At the time they would make it any custom size or shape for an extra $50. Again, we're talking same quality and type as you have at home, so not cheap, but wife couldn't sleep on the original one so it was worth the money.
2011 Coachmen North Ridge 290RKD 5'er
2005 Dodge quad cab dually diesel 6'spd manual
1 weird cat with an occasional attitude problem.