I’d definitely look at extended rear facing seats, especially if your girl is tall, otherwise she’s likely to outgrow before it’s safe to move to the next stage. Don’t be put off by the fact that they aren’t usually 360 seats - they have lower sides so later down the line she’ll be able to climb in herself. Britax are great and quite affordable x
We go for extended rear facing seats as our babies are also chunky! I’ve got a Britax Maxsafe Pro in my car and an Axkid Movekid in my husband’s car. I also have an older Britax model for my eldest in my car and an Axkid Minikid 2 in his car. I really rate them all! The newer seats go up to 36kg and our older ones are 25kg seats so they should fit in them until they’re 5/6 and can go in a high back booster.