I'm replacing a 20 year old mattress used by at least five previous owners. My coach will accommodate a Queen size mattress but I want the "short" Queen, something like 60 X 75 or 77 (Queen seems to be 60 X 80). Having trouble sourcing a good inner-spring mattress in the short size. Camping World has a short queen but it comes delivered in a box 16 X 16 X 60. How much support could that mattress offer? We are going to be full-timers so a good mattress is essential. Any thoughts? "Sleepless in Los Gatos"