We had a Casita 16 SD before we bought our 21C ... The 21C's bed is basically a Full XL, which is 54x80", 6" narrower than a queen. I'm 6' tall and sleep on the street side of the mattress, my wife is 5'1" and sleeps on the curb side. We use Full XL mattress pad and fitted sheet on the bed, and a queen comforter in a 'duvet' cover, which is basically two sheets sewed together with a zipper or buttons at the foot. The duvet doesn't have to be tucked in, and I can skinny out the foot of the bed without waking my wife to do midnight bathroom runs, when I get back in bed, its easy to 'flip' the duvet/comforter back over my legs and bod. Since the queen duvet is 6" wider than the mattress, we both get enough blanket.
We did a 4 month 10000 mile road trip in Mexico last year, and were comfortable the whole time. I could live full time in the Escape (yellow stars are where we camped).
The Casita SD was basically miserable for the two of us, my wife is claustrophobic, and insisted on being on the outside, which meant I had to climb over her to make those midnight P runs... the Casita Spirit dinette made an awful small bed for my 6' long bod. OTOH, the couple times I took the Casita 16SD out alone (astronomy trips my wife found annoyingly boring due to the dark enforcement), it was just fine.