I did the same thing when I had my kid so I speak from experience. Let my wife get a 4dr sportwagen for this purpose since my GTI is a two door. It was pointless. By the time they can walk, they are climbing into the seat themselves. My kid is about to be 5 now and i take him in the GTI all the time. He has his own recaro seat in the back middle that he clambers up into by himself. In fact if I even help him get into it he gets mad, he wants to do it himself.
So the procedure is basically, open drivers door, pull latch on seat up and move forward he climbs in and we get going. Easy.
The other thing a lot of people dont think of when they go this route is that if you want your kid to be safest you have to put the car seat in the middle, regardless of how many doors you have. So if you get a 4 dr and put your kids seat in the middle you end up having to go through the same inconviences that you would with the 2 dr, bending over, reaching in, latching buckles etc.