I found the best thing is a one piece fleece bunting from Lands End. It is not bulky but keeps the child very warm. The arms and legs can fold over to cover hands and feet and there is a hood attached as well. The baby fits fine in the car seat still and will stay warm in the stroller outside too. It's the only thing we used all winter besides a tight fitting cap on under the hood on really cold days. I've used them with all three kids and think they are worth every penny ($40-$45). Order on line and consider buying it a little on the big side so it's roomy enough for all winter. They grow so fast at that age!