I have been using a 3M WR410 adjustable wrist rest, but it looks like those are hard to find. Might be able to acquire one, but from memory they were not very cheap.
You might look at the other 3M offerings right now, their quality is great and the one I am using has been under my wrists for well over ten years, and has held up extremely well. They have two different materials inside, with the gel being the most compliant. One thing I really like about the 3M is they use some type of "silky" covering, easy to clean and very tough. Other manufacturers tend to use some polyester material, which does not clean or hold up well. Also most wrests tend to be curved on top, and flat definitely gives you more freedom of movement.
Of course, YMMV............Later