Hi praise for the poster who mentioned putting foam at the head of the short queen mattress to lengthen it! I felt truly stupid, as in "why did this not occur to us", when I read it because we do custom upholstery and have lots of leftover foam strips lying around.
BTW, that is an excellent resource for finding foam for this type of project. Most upholstery shops will either give you such scrap pieces or charge a very nominal fee. And it doesn't have to fully cover the top to work.
However, we don't have enough clearance at the foot of the bed to resolve the problem by adding 6" of foam at the top. So instead I added 3" of foam at the top and changed the pillows. Standard pillow depth is 20", but your head never uses all of that. So I cut the pillows down to a 16" depth, which was plenty for head comfort, and that effectively gained the additional length we needed.
DH was delighted when I showed him and he tried it out. That resolves one of our two biggest complaints about the livability of our coach. Oh, that all of them took so little time and money!