I thought an easel might do the trick, and went to my favorite art supply store to check out their selection. Unfortunately, they do not have a section called "Small, inexpensive, tabletop easels that can be oriented upright, horizontally, or somewhere in-between for Jackie." The young man who helped me was great, as always, and was quite sympathetic about the shoulder pain. He showed me a couple of stretches that might help.
In the meantime, however, what to do? Then I remembered the bed trays we got as wedding presents.
I got one down and it fit perfectly on my worktable. It even inclines.
Ta-da! Less strain means more work.