I have an original mini from 1976 with two doors and never had a problem with the infant seat. The convertible seat has been a problem though, and we did manage to find one that fit, but it was tough. I would speak with the mini dealer and see if they recommend one. Many carseat manufacturers like britax list which cars their seats are compatible with, at least here in europe. I have a britax two way which is not available in the US market, but it reminds me a little of dionos radian but not as large.My friend has a new mini and uses a maxi cosi. My mini is quite roomy on the inside and can imagine that the new countryman is too so you should be able to find one that works. if you need a little more room rearfacing, you can put it in the middle in the rear and then it somewhat has more space between the seats, or even on the front seat with the airbag off. Studies in Sweden (which has the fewest traffic deaths in the world for kids and we have to rear face until at least age 4) show that it is just as safe if not safer because the mother does not have to take her eyes off the road or do anything great to help the baby. We also crash test at much higher levels than the US. Almost All parents do it here but I am not sure you can turn off the airbag. I have a place in my newer car where i insert the key and turn it off. The new minis are BMWs and they can do it, so you should be able to. Good luck!!!