First time mom looking for car seat advice

So I know not everyone has the same vehicle as mebut just looking for a little help here. However before I get to far into this getting rid of my car for a new one is not an option.

So I own a 2000 mustang and not quite sure if anyone else here has ever found the perfect rear facing car seat to fit. Been doing some searching already because I know it is going to be a difficult task, thank goodness im only 10 weeks in right now. However I was looking to see if any of you mothers out there have any advice for me , or just words of wisdom in general.

Thanks ladies!