Thank you all for your kind comments and helpful suggestions regarding my carpal tunnel issue! I have taken some measures meanwhile (for once, this does not relate to psychological measurement theory I am dealing with every day otherwise ).
For working, I am alternating the rocking chair in the kitchen …
… and the sofa bed in the living room, so I have a change between sitting at the table (straining for the arm, but relieving for the back) and working with my laptop standing on a tray in front of me (relieving for the arm, but straining for the back).
I got amber oil for slathering on my arm, for irritated nerves and aching muscles.
When I sit at the table, I put my arm on a cushion so my arm does not lie on the hard table surface. This little cushion I already had when I was a baby, and while it is too small for putting my head on it now, the size is just perfect for a table cushion. So, the times when the little cushion had merely decorative functions in my bed are definitely over.
All of this has helped to make it a little better already, and extensive piano playing may also play a role in that. The prickling and numbness are still there, but they are not getting worse, and I do not have pain. And all of this is while I have not even reduced my productivity, what makes me happy a lot.
Thank you all again for your kind concerns!