If you have just picked up a brand new MINI then there is the ability to disable the air bag yourself with the key
If its a used MINI then you might not be able to do this.
As for a definative list for what fits the MINI, no, there isn't one, and there should be either.
A car seat should always be tried in the cars that it will be used in before it is purchased, as each and every car differs slightly, even between the same models and the same build years. How the car has been used can effect the shape of the seats, such as if the back seat has been down and its been used to carry things, or if an over weight passenger has sat in the same spot lots, all these things compress the foam of the seat. Also suppliers of components change all the time so there can be variations that way.
you must always try before you buy a car seat, and not just buy one because someone tells you it fits without testing it.
Also its important to get a seat that you can operate easily so that way there is less risk of it been fitted incorrectly
Have a read of
this thread and then get yourself off to a good Nursery Retailer, such as an indepentant or John Lewis
Oh and welcome to MINI2 and congratulations on the great news