Used a full size 6" queen foam mattress from IKEA. We love it. Going on 7 years with it on top of the stock innerspring mattress. Many grades to choose from. This one cost about 300. Initially, in a previous TT, it was on top of the stock short queen mattress, which was slid down the 6" so the foot end of the mattresses mated up. I hateed to have my feet hanging over the end. The overhang of the top mattress at the head of the bed was unnoticeable, since it was 6" thick. Wouldn't waste my time or money buying a short queen or having one shortened. 6" is not a big deal, unless...!
2016 Flagstaff 27VRL Emerald
2014 GMC 2500HD CC 4X4 6.0L