E.S.
Since you've already gotten plenty of recommendations about the carseat, I thought I'd give you another alternative to the bulky jacket in the car seat. Like others have said, you can layer clothing. Also, JJ Cole makes a cozy carseat cover that zips around the outside of the carseat - there are two sizes, infant and toddler. Or just bring a blanket from inside the house to use until the car warms up.