KW have to be the guys to go to if you want to alter the height or rigidity of your car, as their aftermarket products are among the best on the market.
Recently, the guys from KW launched 3 new coilovers for the BMW 4 Series convertible.

While all do a great job of improving stability of the car and lowering the height, each one differs a bit. As such, the Variant 1 coilover is a rigit one, not allowing the user to modify the height of the car. But this doesn’t make it any less good, it just caters to a different kind of alteration.
The other two coilovers allow for some height modification. The Variant 2 coilover from KW can be modified by 16 clicks. The Variant 3 coilover will only allow for a 12 click adjusting. But whichever kit you go for, you can be sure you will have an improved ride for whatever other mods you want to install.