Have you tried the Eskadron wraps? I don't know if they are 100% cotton but used them on my boy when he was on box rest for a ruptured tendon and was very pleased with them.
I got some stable wraps from Equestrian Outfitters I can't remember whether they were 100% cotton or not but were really good quality. Sure if you emailed them they could advise as they often don't give a clear list on the products themselves.