Is this only for Tirano st. Moritz, or also for the way back? You may want to just buy a saver day pass first, which will cover you both ways, and then add reservations seperately.
Remember:
You need a ticket, or something that stands in lieu of a ticket (like a day pass) always.
You need a reservation only if you want to sit in the panoramic cars of the Bernina Express. For the normal cars at the front, and the other trains you do not need reservations.
