Thank you for your request.
For 3 trips, I recommend the Swiss Travel Pass (or the FLEX if you stay 1 day in Zermatt or St. Moritz) or the Saver Day Pass. You can buy our saver day pass 60 days in advance. Beware of the conditions!
The Swiss Travel Pass FLEX 3 days cost CHF 267.00 per person, the Swiss Travel Pass 3 days cost CHF 232.00 per person (4 days CHF 281.00).
This is correct, the Swiss Travel Pass FLEX is more expensive than the Swiss Travel Pass, because you can choose the days of travel.
Don't forget to make a reservation for the Glacier Express.
I hope I have been able to help you and wish you a happy new year.