If you can get away without having to walk around the end of the bed, you could replace the plywood on the flip up storage lid with a piece a bit longer so it overhangs. Then get a new regular length memory foam mattress and cut it shorter to suit. We cut a regular 80" foam mattress to a short queen size and just use regular length sheets.
Personally I think those entertainment centers are a waste of valuable use-able space and a curtain on a track would be better. Sometimes the viewing angle of the TV is poor from them too, as in our friend's TT.
