Re: Baby Seats
Do a search, as there were a few posts about this a while ago.
If you want the absolute best fit, the Britax Duo isofix seat is about the smallest that I found, and much easier and safer than faffing about with the seat belt. I have one in my GT
I took the headrest out for a couple of months at first, but I put it back in a while ago, and the seat still fits really well, much better than with a belt.
You won't find one that fits under the headrest due to the design, so removing it is an option.