Replace your shocks. Standard shocks are good for 30K. Put some KONI
brand in there for performance, BOGE for  ride.

B.D.

A 95 even with minimal miles is definitely going to need new shocks just
from age. Boge worked well for our 95 XJS, but Bilsteins are also nice  if
you can find the right model for performance. Im not sure they were
available when I shopped around a couple months back. Koni I would consider
way too harsh and more for semi race cars , Japanese imports or tuner cars.

The ride is now tight, but if it is luxury you are looking for the XJ ride
is always going to be more luxurious. The XJS is a little more sports car
oriented. Stick my XJ12 and XJS together and the XJ12 with sportspack
suspension has the better overall ride, but the XJS out corners it.

Daniel
1994 XJ12
1995 XJS 4.0

Rowen,
Come on man, you can be a bit more methodical than this.
First there exist suspension specialists who can dynamically test your
shocks.
If they are anything other than spot on replace with whatever they
recommend, shocks are not particularly sophisticated & you should be able to
select a suitable unit to suit your ideas of what the rear should feel like.
Occasionally stock shocks need modification to suit particular cars which is
a bit more costly.
Same goes for coil springs, they can be made stiffer & lower if you desire &
the cost is modest.
Ensure your rear tyres are selected from one of the well known better brands
with compound & pattern to suit your motoring needs.
Finally the XJS is not one of the worlds great handling cars but it should
feel tight, composed, predictable, & comfortable.
Good luck.
Pete