I'm sorry to hear you're in pain Glen and Shoe. Pain can take all the joy out of writing.
It sounds though, Glen, as if you are a competent touch typist, so what worked for me may not work for you.
I'm also 66, and following a couple of minor strokes ten years ago, was left with crippling neuropathic pain in my left arm and leg. I was prescribed Pregabalin, which I still take.
Never a touch typist, I used to hunt and peck my way around the keyboard, but it was a painful process until a fellow writer suggested I try a Dvorak layout.
Sir had already bought me a mechanical keyboard, which helped a little, but put together with Dvorak it was a complete game changer. I am now a touch typist - although I do still make mistakes, due to my fingers juddering and skittering on the keys - and can achieve a pretty decent speed at times. What's more, I can type for hours - pain free!
It only took me a week to learn the Dvorak layout. When I started, Sir bought some letter stickers that covered the keys on the keyboard. Now, I don't need them. The keyboard settings have been changed to Dvorak in Windows and I merrily type away on a Qwerty mechanical. Bliss!
If you'd like to give it a try, this is the site I used:
https://learn.dvorak.nl/Good luck. I hope you find something that works for you, whether it be pads, posture, layouts, or medication.