Serious question...how do you dress baby for cold weather.

Okay so I'm clueless and this sounds really silly, but the mornings here have been so chilly. The other day I put a hoodie on him and he looked like he was uncomfortable in his carseat and it was very hard to get him buckled in and I know you shouldnt let them wear bulky clothes in their carseat. Today I had him in just a onesie and some long pants and socks with a fluffy blanket over him but he pulls the blanket off his arms and tries to pull it over his head. What the heck do you do? I have one of those fleece covers you put over the carseat but it gets into the 70s by the afternoon. Help!