back pain and particularly while in a Morgan seat can be caused by a number of things so it's difficult to prescribe a solution accurately
However
The vast majority of people with back pain have some issue with their lower back and some sort of a disk problem
I can recommend a book called 'Treat your own back' by Robin McKensie - on Amazon quite cheaply
The problem with Morgan seats I find (like many car seats) is that there isn't enough lumbar support to keep the spine in the double 'S' position to relieve possible lower disk problems
I would recommend a more pronounced and adjustable lumbar support
I have used one of those cheap mesh supports but it rubs the leather so now I use the opportunity of driving the Morgan to do my back extension excersises to firm up the muscles in the lumbar area - ( the excersises are in the book) and this has worked really well
