Hello yunka
It is too early to book one-way tickets now. We, the Swiss, do not book tickets that far in advance.
From 07.07.2024 to 12.08.2024, there will be engineering works on the line you are intending to take, requiring the total closure of a railway tunnel, which affects all trains going from Basel to Bern (and further to Interlaken). Certain trains will be rerouted, but the schedule for the rerouted trains is not out now.
The cost for a single flexible full fare ticket from Basel to Interlaken West is CHF 64.
You could purchase a full fare Saver Day Pass now, which starts at CHF 52 depending on the day. The cost for the Saver Day Pass is raising the nearer the travel date. It is valid for any train on the day of validity. Just keep in mind that Saver Day Passes are not cancellable; if you purchase it now and there will be changes to your travel plans later, you will lose the ticket. But, still worth a consideration, see here:
https://www.sbb.ch/en/tickets-offers/tickets/day-passes/saver-day-pass.html
Kind regards,
Roland