There's not much you can do. Firstly, all the suspension bushes and joints should be ok. Perhaps reduce your tyres pressures to a minimum 32psi front and 30psi rear. More pliant tyres which focus on ride quality are an option, and lastly, and most expensively, change the suspension. However, Autodelta don't do a comfort suspension ofor the JTD. You can view a thread about 147/156 suspension here.
as above, dampers. i recommend KONI Sport. they are adjustable for 'rebound', which is not as technical as you may perceive. you can set them to your liking.
i have used KONI Sport on many cars, including the 2L 156 and on my V6 GT.
i have just fitted Bilstein B6 dampers on my 2L TS 155. it's early days (literally had the first drive today after fitment), but they do not feel nearly as comfy as the KONI's, and i cannot adjust them either.