Cold room

Any tips on keeping a room above the garage warmer? My husband swears that it’s the window, but I feel no cold air coming from around the window. The floor however is freezing. It never really gets above 65° in the room. I don’t want to use a space heater because they can be dangerous. But this is my infant son’s room. He’s only 9 weeks old. And it’s so cold in there in the early mornings. I’m at the point where I’m ready to ask my dad to cut holes in the garage ceiling and insulate it since my husband won’t. But that will just start a fight. It’s already snowed where we live. It’s only going to get colder. But apparently it’s too much to ask for a safe, warm sleeping environment for my son.