From our experience, as long as you have isofix and are reasonably fit then it's OK. We use the maxi-cosi cabrio on isofix base - dead easy to unclip the seat and lift it out (you quickly work out the angles so not as to bash the baby off the back of the seat/roof!)
Katie is 8 months now (and just under 16lbs) so we now tend to take her out of the seat (rather than remove the seat altogether). We find it easier to climb into the back seat, lift her out and then carry out the driver's side. Not ideal being on the driver's side I know, but no different than a practical Clubman!
Pram wise, we went Bugaboo Cameleon (clip wheels off and it fits in the boot with space to spare) which made a travel system with the car seat. We now have a Quinny Zapp too which is specifically for the MINI.
Good luck for December - hope all goes well
