He is at a small family daycare now. We love it, but he is really outgrowing it. In my state free, universal preschool is offered in the 4 to 5 year, but almost never at in-home places. This means that if we want to take advantage of the free schooling and if we want him with age peers, we need to go to a larger center or preschool of some kind. If I thought the place where he was would continue to work, I'd keep him there in a heartbeat, but she doesn't really even take kids that old.
Okay, not an easy decision to make.

Phew. Are there public preschools? (I'm thinking you've looked and either didn't like them if they exist or they don't exist). But, just asking.
Did your day care provider have any suggestions?