You need the retrofit harness from bms, also a sport steering wheel, airbag and mf buttons.
The install wasn't too bad, however wiring the harness was a pita. You can pm me if u need more info, I did it on my old 335. I also have the bms manual as well if u wanna take a look at it.
07 335xi- (2007-2010)
08 Legacy Spec B Fully Built (08-)
09 335i (2010-)
15 X5 xdrive 35i (2015-)