rough riding

[eds2003bmw]

Hey folks! I own a 2003 x5 which I bought last year And I've just about had it with the rough suspension,its very bumpy. A friend suggested I replace the rear bags with springs but he said it would also lower the height of the vehicle. are these comfortable,I mean, more than the factory bags? Is there any way I can have the dealer adjust the bag pressure making them more confortable? I have on the vehicle 19 inch chrome bmw rims and low profile tires, the manufacturer asks for two different sizes of tires on the vehicle's front and rear. please ,anything helps.