On all cars, I stick with the famous Little Tree air fresheners. (I love the True North scent. Not tarty or too fragrant.. just a nice clean scent. All my passengers
it) Peel the plastic wrapper back half way, place under seat and after 2 weeks, peel the whole wrapper off.
As for washing it… Depends on your budget, OCD level, but I’d highly recommend Obsessed Garage’s YT channel / store for tips, products and more.
And one note - I don’t have my M3 yet but have heard the seat perforations
may be an issue with cleaning, I wouldn’t drench the seat as the liquid may be hard to extract afterwards. Guess we’ll see with time.