It does sound very niche indeed!
Taking a shot at identifying the problem here. Might be completely off?! As I don't know the details. So bear with me.
Thinking all the countless hours of code has been taking it's toll over the years.
And I'm not really sure smaller adjustments to your keyboard setup, would provide any major and permanent improvements to the theoretical situation.
I might suggest a focus on physical training instead. Fingers/hands, arms and back training. Maybe a standing working position. Or laid back. And changing positions.
I did have some carpal tunnel problems with extensive mouse usage years ago. Physical training and a paradigm shift from mouse to wacom board did the trick.
Or if that's not the case. It's probably the route of.. just order a bunch of stuff with the best reviews and see how it performs with your setup.
Did you contact eg. Føniks Computer or Labtech?
Others??