Needed Item

We recently moved one of our cats out to the backyard to be an outside cat. We have just tried too many times to get him to use the litter box. Right now, he seems to be doing fine. However, winter is coming and I'm worried he can't stay warm. What would be nice is if I had an electric blanket that he could sleep on in his crate. However, I haven't seen one of those in a long time and I don't even know if you can buy those anymore. I just think it would be nice for him to have something I know will be warm in the winter time.