How to figure out the appropriate rail pass

We are preparing to visit that area for the 3rd consecutive summer, (absolutely LOVE it)! I have crunched numbers and have decided that what works best for us is to purchase 1/2 fare passes and then Jungfrau Travel passes for the appropriate number of travel days. The 1/2 fare also allows you a discount on the Jungfrau passes.
https://www.jungfrau.ch/en-gb/jungfrau-travel-pass/
The convenience of hopping on and off cable cars/funiculares without waiting in line and buying individual tickets is worth buying the pass.

For Basel to Mürren buy a Supersaver ticket in advance for further savings. You can safely buy one for a train that leaves 10 minutes after the arrival of your train from France, as your connection will be protected.
Some for Mürren - ZRH. Buy a Supersaver ticket, or a Saver Day Pass in advance, whatever is cheapest.

You can buy all that now.
For such a short trip the HFC is probably not going to save you money.

Wengen I has it right in your arrival and departure ticket best options as long as you can commit to the schedule.

Since you are staying in Mürren, you might benefit most from a Berner Oberland Regional Pass for 4 days. https://www.berneroberlandpass.ch/. Uncpair right about the convenience and flexibility with having a pass. You won’t have to think about it and can ride anywhere in the Berner Oberland on a whim. Only the highest peaks will incur an additional charge.

The Jungfrau Pass recommended above does not include the cableway from Stechelberg to Mürren thru Gimmelwald and you will probably want to use that route.

Thank you all! Do you recommend buying the BO Pass in advance, or buying it upon arrival in Switzerland?
We can definitely commit to the Basel to Murren ticket; I was thinking of waiting to purchase the ticket to Bern to adapt based on weather.

You can buy in advance and download to your phone as a PDF. If you buy in person, you’ll get paper tickets. Your choice, but I sure like being paperless.