My OH uses a bendy straw in a lidded mug with a hole for the straw. If the shakes prevented him getting the straw in his mouth first time it would swing away. Then he had to use two hands, one for the mug, one for the straw and that was its own problem.
Then I cut a length of plastic, from a yogurt pot, punched a hole in one end with a desk hole punch and used an elastic band to fix it to the mug. I pull the plastic down until the straw is at the angle he wants and it stays there.
Hope it makes life simpler for you too.