I have the queen corner bed also. (Sunseeker 2450). I put a mattress cover on and work my way to outer corner, then follow with the fitted sheet. I then put my duvet cover on (you could use comforter, quilt, etc). I don't use a top sheet at all. Once you get the fitted sheet on that part is done until you have to launder it. We actually sleep on top of the duvet cover and just cover with throws or other quilts, etc. Then in the morning you just fold up the covers and place at head or foot of bed and it looks neat again. I, too, am 62 with a bad knee and a really bad back but once you get the fitted sheet on (which takes a max of 5 minutes), you're done for the week.
Also getting the memory foam and just making it is another excellent idea.
I really don't mind the corner bed and I have plenty of room to get out at foot of bed without disturbing my husband.