Off hand I would say springs to.
However, my only experience is with my Volvo that had a low ride hight with some bottoming out in the rear (going up driveways).
I replaced the rear springs and gained several inches of heigt and the Car Felt and handled better too.
Someone more experienced will have to tell you if the Ball Joints alone can cause your problem.
Also the FSM has specs for the Ride Height. If someone would post them this could give you a clue as to if the springs need replacing.

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84 300D, 82 Volvo 244Gl Diesel