Who are we? In order to give you advice, we have to know more about your travel party.
For adults, I suggest a full fare Saver Day Pass, which is available from CHF 52. The price is raising the nearer the travel date: Saver Day Pass. | SBB
For the way back, you could again buy a Saver Day Pass.
Please kindly note, Saver Day Passes are not refundable nor exchangeable. They need your passport upon ticket check in order to be valid.