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try something like this https://www.amazon.com.au/Kikkerland-iBed-Desk-Wooden-US039W/dp/B00MW58G2A
put you mouse and as much of your arm on top of the tray. Try the tray on the table and at worst on your lap. It helped me doing 8 hour diablo 2 sessions with no pain.
Thank you for the suggestion, but unfortunately I don't think that would have space for a keyboard from my understanding.
There are trays such as this with little divets in the wood where you can pop the tablet into so it stands, but I'm just a bit concerned buying stuff like this at random from Amazon, because from my experience the quality can be a bit all over the place!