Disney doesn't rent air mattresses at any resort, and they don't provide any additional bedding at the DVC (deluxe villa) resorts. You'd have to bring your own air mattress and any bedding you wanted. There's usually an extra blanket and pillow in the closet in DVC villas, but not extra sheets.
If you don't want to carry all that with you, you could ship it to the resort ahead of your stay. If you'll have a car, some guests will swing by Walmart or Target on the way to the resort and pick up a cheap air mattress and bedding to use during their stay, and just leave it all behind when they go home.