Personally I don't go more than 4 or 5k between changes but it is your car and your choice. Is there a severe service schedule for the Mini, follow that if there is any city driving involved.
If you decide to go with the factory recommended interval, please get into the habit of checking your oil on a regular basis (once a week maybe). All cars use a little oil, consumption that might not be noticed in 3 or 4k miles, might be fatal over 12k miles.
When you check the oil, it's also a good time to check the other levels, i.e. coolant, brake, and transmission. For example, drops in coolant level on my 2000 Blazer were due to a leaky intake manifold gasket and a crack in the radiator on separate occasions. Both repairs were a few hundred, however if not discovered repairs would have been in the thousands. Recently, I discovered the air filter lid had come loose on my 2010 Cobalt, again an easy fix.