You should go with 19" wheels, they fill up the wheel wells perfectly since the e90 is a bigger car it looks so good.
Dont get Miro M6 reps. They are not very strong and have had some issues with quality.
I would really recommend some Avant Garde M310's, they look so clean and very un-civic like
or the Avant Garde M341
Let me know if I can be of any assistance