Looks like no one wanted to 'commit' to an opinion so I'll wade in
OK, having had a 5er in the distant past with twin beds, found that they worked very well as they were extremely easy to make up particularly if you don't have a bedroom slide. A queen or even a double ends up being fairly difficult to move around to put bedding on or as you get older, navigate at some dark hour with the usual limited space. Later 5ers will have at least one slide and often two which makes the queen or even a king a good choice. Our current 5er has a full queen, it's very well situated but there is that other 'thing', a DW with restless leg syndrome which makes me wish for twins and something we had two go to a few years ago in our home.
If you really want a queen, then tear out the twin platforms and build one for the queen. Very simple if you have a few tools and a weekend. Some 2x2 dimensional lumber, a piece of paneling and a piece of plywood and a bunch of screws. Yep, you might need to recarpet, but in the scheme of things, fairly inexpensive with rug store remnants being pretty reasonable.
Then mattress(es) - cheap junk is not always the best way. You will spend about 1/3rd of any weekend there so comfort has to be considered. We have a pretty high quality one in our 5er - a LOT better then the junk Keystone supplied as OEM. We both usually sleep pretty well.
Disclaimer: MY opinions based on MY experience