I will be traveling from Paris to Lauterbrunnen on Saturday then back to Paris on the following Tuesday. I'm thinking that I will just buy a ticket on the TGV from Paris to Bern and get the Swiss Pass for 4 days to cover my travel within Switzerland. I don't know exactly my itinerary once in Switzerland but I definitely plan to go to Jungfraujoch and also visit Murren and Gimmelwald. Does that sound cost efficient? I'm leaving for Paris on Wednesday. What should I buy in advance? Thank you!
Yes, that sounds a good plan, except you should have bought your ticket from Paris to Basel (the Swiss border) weeks or months ago. The cheapest seats are now gone. Prices are now between €64 and €120 each way, for the dates you listed.
You can see the times and fares, and make bookings on: https://www.tgv-lyria.com/en
You can also by your Swiss Pass online on the SBB website ( https://www.sbb.ch/en/ ), that will save you having to buy it at Basel. And if you are already in Paris you may have a problem with printing your tickets.
Thank you Chris!