Its important to know whether you have a "level control system" because "the sag" can go 2 ways.
If you have a level contorolled car there are more questions than if not... to identify this check if you have several lines running towards your strut ...one from the front & one from the back to the pressure reservoir and one from it to your strut. If you have these then changing your shocks may be pointless and I'm sure someone the wiser will explain.
If you don't see these then changing your rear shocks may be the answer.
Before all this make sure your tires are the same height 175/185?