One good way to make sure you're not straining any part of the body too much is to have multiple confortable positions that you can change from along the day.

The ultimate good-for-you background activity would probably be some movement equivalent to climbing a tree (pumps your whole lymphatic system; suspected of being a causal factor of the health of people in “Blue zones”, as said zones all contain a lot of orchard workers; something our bodies probably expect us to do a lot of, given our evolutionary roots; etc.)

I’m not sure how you could combine it with typing, though!