Take a look at some used BMWs on your dealer's lot. You'll probably find many high mileage BMWs with like new steering wheels. These things are designed to be touched and caressed every single day. Putting a cover on it totally ruins the aesthetics and feel that BMW tries to perfect. If you are really freaked out about it then plan on buying a new wheel in a few years, there are some awesome suede BMW wheels with flat bottoms and shift lights that you can swap in.
Heck I'd even argue that a cover could cause premature wear faster than no cover at all. The friction of the cover moving over the wheel over time can't be good, let alone the dies that may leech into the steering wheel from the cover interacting with your sweaty hands.
But based on everyone's comments here you might be the ONLY M Sport owner in the history of the F30 M Sport that wants to cover his steering wheel. Just enjoy it and quit worrying. Focus your preservation mentality on other wear items that are seen every day. Maybe install a clear bra if that's your thing, have some clear coat protectant added, scotch guard your carpets, but really cover the steering wheel?? How are you going to protect your leather seats? They are gonna wear much quicker than the steering wheel.