Lowering won't solve ride issues, and may actually make them worse (as you're giving the struts less room to move before they hit the limits of their movement).
It sounds like the existing suspension is underdamped (not uncommon I believe) - adding weight to the car is increasing the effective damping rate due to inertia, and this is increasing the effective damping rate.
At 115,000 the original suspension is probably past its use-by date. I'm currently in the process of replacing the stock suspension in my 2003 Bora V6 4Motion, and the current front-runner is a Koni FSD kit with matched struts and springs. The alternative I'm considering is the Koni Sport struts with matched Eibach springs. Both Koni options will lower my car by about an inch apparently, but that's a side-issue - the important issue is the matching of strut and spring rates to provide a properly tuned ride.
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