You can also play mountain dulcimer with the instrument on a table or stand rather than on your lap; experiment and see what works best for you.
by the way, the first time I went to a Nonsuch weekend I shared a room with a woman who had taken up hammered dulcimer because of an arthritic condition - she found hammered dulcimer the least physically stressful instrument to play (though it would be harder to learn than Appalachian mountain dulcimer). Have you had a taster session with hammered dulcimer yet?