We bought double bed size cotton fleece sheets and shrunk the heck out of them. Once shrunk, they conform to the cut corner of the mattress shown here. The pic is not of the sheets, but of the fitted mattress cover.
We have a corner bed in a 24' model and have a full size queen 60x80. Regular taut fitted queen sheets work fine as they do at home. We bought a decorative sheet set to compliment our interior and just use the bottom fitted sheet and matching pillow covers as we make the bed . We just fold up and store the top sheet and a blanket to use as needed at night. Doing it this way eliminates having to make the bed everyday while keeping things looking neat and tidy.