Your situation reminded me of Sasha at that age, she use to do the
same things! not stay still, climb to my shoulders, shake like a chihuahua.
but I didn't like it so much when she used to climb to my shoulders, especially if I was driving.
now she is older (9months) and she loves the car rides to stick her head out the window and feel the wind.
It will stop with time but I think the snoozer car seat or a small kennel is great idea. It will be more secure for your yorkie in case of a car accident and the airbags deploy.
below is a link for the snoozer car seat
Pet Car Seat: Pet Car Booster Seat Lookout for Small Dogs at PETCO