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 (07-10)
08 Legacy Spec B Fully Built
09 335i (2010-)