m-tech mini one.
The exhaust system on the Cooper has an additional intermediate silencer.
Altering the ride height, final drive and adding a rear anti-roll bar will not be easy, and will affect your insurance. Easier to trade in your One and buy the real thing
I don't mean to offend Mini One owners - its a fine car. But if you want a Cooper, it doesn't make sense to me to get a One and then modify it.