Hello Heajueghie87
Welcome to the SBB Community!
Simply enter the depature and arrival point in the trip planner and see what the ticketing system suggests as a ticket. It might be a point to point ticket, or a Saver Day Pass or even a Supersaver ticket (e.g. Zermatt to Geneva Airport), all at full fare.
Your itinerary looks like a checklist: been there, done that.
Day 1: Bellaggio to Tirano to St. Moritz? All in one day?
Keep in mind, August is the vacation time in Italy. Locals and foreigners flock to the mountains and to the beaches for vacation.
Kind regards,
Roland