I don't know where you live, but in Ohio it's 9º my young man is a 7yo pug named Bruce and he gets very few pleasures in life beyond his association with me. I plugged in an old heating pad (i've personally upgraded to heated blanket) and put it on his bed-- he's in a state of euphoria.
(fyi: goes without saying, don't make it too hot and don't burn your house down. cheers!)