We do not want to take the bus portion of the trip into Italy...been there. We'd like to leave our rental car in a town that we can return to for overnight while we take the Bernina Express. Would you suggest going all the way to Tirano, and returning to one of the above cities on the regular train?
We covered this area & N. Italy by train well. Tirano is a non touristy town but a good hub for getting the scenic train to St Moritz area.Suggest you get a hotel there to keep your car for safety. The views on this route to Switz. are beautiful. Overnite in picturesque & reasonable Pontresina but walk around St Moritz half day.