If all you want is a smooth ride, then get the BMW factory shocks/struts, and springs. The strut is the front "shock" assembly which includes a shock looking like thing (but its called a strut), and you also have a spring there--the rear has springs and regular shocks. That's a simple explanation.
You could also go for Bilstein touring shocks/struts. Bilstein has excellent reputation ( i think they do the original factory shocks/struts for BMW), and the touring version is cheaper, though not as responsive or sporty as the stock units, if I understand correctly. The dealer will cost you a lot of money, avoid unless you just don't care about money.
Find a competent independent BMW mechanic and get the parts and installatino through them. That way it's all warrented, etc...
Good luck. Nice looking car.
98 328i, black/black, manual, canadian sport pkg, ECIS intake, koni sport adj's, dinan springs, oe/oem clears.
Considering: tms shark,M 17" wheels, larger sway bars.