Have you tried Sally's Beauty supply. They have soft rollers you can sleep in but I don't remember how large they go. If not Sally's in your area, maybe a beauty supply store might have them.
Have you tried the Carusu Molecular Hairsetter? I have super straight hair that won't hold a curl using hot rollers or a curling iron but it curls like crazy with the Caruso. It uses those spongy rollers and steam with dry hair and the curl is amazing.
I would try beauty supply, I sleep in smooth plastic rollers, once you get used to it it's not so bad. Key to sleeping in rollers is how you secure them. I use a wave net tied tight with a satin slumber cap over it. I used scarfs for doing gardening or errands, but they do work as well as slumber caps for holding a set while sleeping
