Hello,
You should visit somewhere professionals can give you advise and try the car seats in your car.
You will still need a rear facing car seat at the moment. There are lots of places you can go, we went to mothercare for our current one but before that we went to a place similar to kiddicare.com.
Halfords I think can also offer advice and fitting but I have never shopped there.
I have always found our mother care very good.
They do grow so very quickly dont they!