So a couple of things. Your suspension is probably shot at 90k miles its a wear item and they wear out... You should probably replace the rest of the control arms, as well as bump stops, strut/shock mounts and strut bearings, and tie rods. This is probably not going to be a silver bullet type of fix.

2nd, what kind of wheels and tires do you have? What inflation pressure do you use? Generally the bigger the rim the worse the ride (adds more unsprung weight). If you're using more than a 19" rim, I can tell you your ride will improve by downsizing. I can tell a noticeable deterioration in ride quality by going to 20" or large rims on this car. I can't tell you how many SUVs i've been in with over-sized rims and its jiggle city.

Ditch the run flats if your using them, and switch to will be flat, this helps a ton too, and make sure your running the door pilar recommend inflation pressure if you still are using stock rims.