Keeping Feet Warm- Any Suggestions?

Ethan has never liked to have things covering his feet: booties-nope, socks-nope, shoes-nope
He takes them off every chance he gets! This wasn't much of a problem when he was younger because it was harder for him to get socks off by himself, and he spent a lot of time in sleepers with built-in feet. But now most of his jammies don't have feet, and he's old enough to remove pretty much whatever we put on his feet by himself. Does anyone have any recommendations of what we can put on his feet (specific brands/styles of socks, shoes, or slippers) to keep them warm that would be difficult for Ethan to take off? Thanks!!