Lowering the car should not hurt the factory shocks.... you should cut the rear shock bump stops so they dont 'bottom out'.....

Needswings carries the Eibach Pro springs and they will get you what you are looking for... I have them on mine with Koni adjustable shocks......

Also note that lowering will increase your negative camber on the rear wheels a fair amount.... this is tough on the inside of the tires..... if you lower the car you should think about adjustable rear camber arms....

(I know a guy that makes some).....