Fit a set of "Puma" 90 springs, and a set of Terrafirma standard length 4 way adjustable dampers.
The Puma springs give a better ride quality and the Terrafirma dampers are adjustable to give a more comfortable ride (set them to the softest setting)
l've done this to a 110 and a 90 TD5 and in both cases there was a definite improvement
My missus (after l did her 90) said it was "like having a mattress between you and the bumps in the road"
You can buy the springs new "take off" from Twisted, or you could last time l looked.