We turned our 2753 sofa into a daybed by removing the jackknife sofa and putting plywood on top of the framework. We then bought a custom foam mattress from Page Foam Products (~$200 shipped). That would work for your bottom bunk. Ideally your top bunk would be a cabinet that fold up and away for daytime so no one hits their head when walking by. Those were common in the older smaller Sunlines. You had a hinged mattress and could leave the bed made up, but fold the whole thing in half to close it during the day.
Lance 1475 "Snoopy"
2012 GMC Sierra 3500HD 4x4 D/A
2012 Arctic Fox 30U, SUNLINES - 2006 2753 "Tweety", 2007 QUE "QUEtSE", 2364, 1660