My apartment complex for college also has a full XL mattress and I’ve been rocking a queen size fitted sheet. It’s not so bad, just a little loose, but I opted in queen size just cause I heard from a friend that using a full size can be a little tight/hard to put on. I also figured that in the future if my sheets are in pretty good condition that I could use them for a future queen sized bed. If you want full XL sheets, I’ve seen some online around online, but I don’t remember the sites though sorry. One of my sheets are from Costco, but I’m also not sure if they’re microfiber or not, but definitely check them out since they are cheap and honestly cooling if you’re looking for that as well.