Infant carseat

How long did your little one fit in their infant carseat? I know it goes by weight and height and every child grows different but our little one will be 8 months (due in feb) at the start of next winter and we live somewhere where it gets really cold. It would be so much easier to put her in the carseat safely in the house and then put something warm overtop. Im getting a little anxious thinking about taking her outside and having to take her jacket off to put her in the convertible carseat and making sure she’s not freezing. Seems like it would be a bit easier with a toddler and I wouldn’t feel so worried about her being without a jacket for a minute. I guess I’m just looking for any tips to keep a little one warm safely in the winter if for some reason she’s too big for her infant seat. We’ve decided on the Nuna pipa btw :)