Your dampers may be worn out, which could make the ride feel excessively bouncy, particularly at speed. Replacing your dampers should ideally solve your problem, giving you a similar experience to when the car was new.
Age can also affect the performance of your vehicle's springs, so you might want to get those checked, too. Also, you could experiment with the tyre pressure to find the ideal balance, as sometimes the manufacturer's recommended settings might not be as per your comfort.
