Our place gets pretty cold at night (well cold for San Diego lol!) The heat turns on if it gets below 50 but that rarely happens. Its usually between 55-65 at night. I put Caleb in a long sleeve onesie then a fleece/terry sleeper and cover him with a blanket. If it's especially cold I put a sleep sack on him and then the blanket, but like yours he's really too long for it now. He definitely has a hard time sleeping if he's cold!