I use a three-inch magic foam topper on both my tent bed ends. When the roof is lowered for travel the top of this mattress actually just touches the ceiling.
Three inches was a great choice for comfort for us...
Additionally we have those 2' by 2' rug carpet squares glued down on all of the wood bed area. In addition to this we also include those 2-inch square by 18-inch long foam pieces that come with the home air conditioner window units that are installed in the home opened window when raised up to install the window units. These are placed all around the tent bed areas where the fabric meets the wood tent bed floor area. This really seals off any draft areas coming from small openings around the tent bed end fabric walls when setup for sleeping..
I also had to re-seal the area where the tent bed floors are pulled out as far as they will go. Our model had a very small weather seal to close the opening between the inside front and rear trailer wall and the tent bed wood floor area. Once pulled out you could bend over on the inside hallway and see daylight in several areas of the tent bed floors where the small weather seal did not fit good. These opening attracted mosquitoes and night bugs into the trailer when it got dark outside and you had lights on inside the trailer.
I used this style of weather seal to slip over the front and rear walls of the POPUP to fix this problem.. The tent bed floors slid over the top of this weather seal as it is pulled out for setup.
Once I started working on the tent beds ends to make thing more comfortable one thing led to another...
We are snug as a bug now sleeping in our tent bed ends (No pun intended)...
ADDED NOTE: Be sure your ceiling lights 12VDc disconnect switch is functional as having those ceiling lights come on after you have lowered the roof might be a fire hazard. Every POPUP trailer I have ever seen has these installed somewhere inside the trailer to automatically disconnect the 12VDC going to the ceiling light assemblies...
Roy Ken