It's easy to find a stroller to fit - heaps of choices there. But to find a propper full-size pram that fits in the MINI boot is a little harder. We went to several baby shops and tried everything they had in the back of the MINI. Only one fitted in our experience and it was the Phil&Teds. Fortunately this is one of the better prams on the market anyway (but not one of the cheapest at around $400).
Regarding baby seats ... we bought a Turn-a-tot on recommendation from a fellow clubMINI member. Very handy while the little one is facing backwards as you can strap them into the seat facing the front and then spin the turn-a-tot around and lock it in position. Much easier than trying to load them in backwards.
Like the other guys said, driving a MINI and having a baby really isn't a problem