31 October 2019
A thin fleece jacket is ideal for the car seat.
A good way to test if your coat is too bulky, is to put your child in the coat, buckle the straps and tighten. Then unbuckle your child (without loosening the straps), take off the jacket, and put your child back in. See how much slack you have. If there is a lot, that jacket isn't safe for the car seat.
If the weather is pretty mild, I'll do a fleece jacket layered with a big coat, then just take off the coat once we get to the car. I am definitely going to look into the car seat ponchos though, they look like the best option! As long as it doesn't compromise the straps, it would be safe.