I have found with the 60 profile 255 tyres, the ride is a little bit softer, but only a little bit. Also, less air should soften that too. A 65 profile moreso I presume.
I know someone who broke his back, and he bought a new VX Landcruiser, which has electric leather seats, etc. He replaced the seats with alternate ones, for his back.
Truck seats have adjustable shock absorbers, to soften the ride especially when a truck which is not a semi, has no load. Bus drivers also have shock absorber seats - they seem to move.
I don't know if you can get such a seat into a Disco.
But you can get an air cushion for vehicles, and they do soften things a lot I think.
Here is a link - the cushions cost around $200. Maybe worth a shot.
A whole seat might be better, but I don't know about availability.
Here's a link on a quick search I did:
Testimonials - Airhawk Australia | Seat Cushions | Motorcycle | Truck | Bus | Car | Heavy Vehicle

