I suggest you to calculate your total cost of journey and then decide if you want to purchase a Half Fare Card as it costs 120 chf, also you can buy it already on SBB.ch and book your trains with half fare. In most case it is worth the money, especially if you are going to do some mountain gondolas.
If you book in advance you will be able to find the so called supersaver tickets, they are discounted but you will need to take the specific train you booked.
If you prefer you can also buy the normal priced point to point ticket, it will be valid for the day and the route you are going to travel on, you will be able to use any train on the booked route.
It is also worth mentioning that with a half fare card you should be able to book the saver day pass ( https://www.sbb.ch/en/travelcards-and-tickets/tickets-for-switzerland/day-pass/saver-day-pass.html ). You will be able to use almost any train, bus, boat and even some selected mountain trains or cablecars freely for one day.
The passes will be valid only for the section in CH.