I have 2 big dogs who sleep on the bed. I have some old extra blankets that are theirs on the bed that they wad all up & kick around & make their "nests" out of. When they decide they have them "perfect" they lay down & go to sleep. Maybe your son could try that & see if it would help. Since I wash all the blankets ALOT on this bed, I don't know if he'll ever be able to have & keep a really nice quilt on the bed without it showing wear. I usually just put a nice one on this bed when I have company & then go back to using an old one for everyday use.
I wonder if something made out of heavy fleese would work as a bedspread to cover up the bed with first & tuck in between mattress & box spring & then the old blankets for the dog to make his nest out of?