As I have been having some cramps after prolonged use of the pen, I’ve decided to do some research. And this is the result of the research, let me introduce you to: Plus Ergo Grip for Wacom Pro.
I couldn’t find them anywhere in UK, so in the end I had to order it directly from US. It has taken a couple of weeks for it to arrive, but it is here now! And I have it fitted as well. It seems quite comfortable, but I am yet to test it properly. If you are interested in a review, please leave me a comment. For now I leave you with a photo of it already fitted.