Is it an Xdrive or RWD? If the latter then you can add Eibach or H&R Sport springs. But they will lower the car 3/4" (for 535i Sport, and 1.5" for 535i standard) and will overstress your stock shocks. To get a proper suspension you would also replace the shocks with Bilstein HDs or Koni FSDs to match the new ride height and rebound profile.
If it is an Xdrive then only KW V3 coil overs will work for that car.
Audio: Jehnert Flatline speakers, Mobridge M1000 DA2 prepro, Helix P-DSP, Zapco Z-150.6 amp, CIC iDrive upgrade
Performance: Cobb Pro Tune, AR Downpipes, ER FMIC/CP, DCI, RB turbos and inlets, KW V2 coilovers, Fuel-It Stage 2 pump w Ported fuel rail, Mfactory LSD