Which swiss rail pass to buy?

Hi Wrenc! All purchase options are displayed at the upper right corner of the Swiss Pass page. Just select your country of residence and the right pass variant for an overview of resellers and prices. Advantages of an online purchase are that you can pay in your own currency and that you don't have to spend time purchasing your pass after arrival, but can start using it right away.

Yes, the Swiss Saver Pass covers the trips you mention, including urban transportation in larger cities such as Zurich. The downloadable validity network map at the Swiss Pass page shows the exact coverage of the pass.

You can plan your trips using the online timetable. The most obvious route from Bern to Zermatt is via Thun, Interlaken, Spiez, and the Lötschberg-tunnel connection to Visp. Brig would be a detour in this case. However, if you like scenic rides and don't mind spending a bit more time on your trip, you should catch the regional Lötschberg express via Kandersteg, Goppenstein and Brig (just add Goppenstien as your via-station in the timetable to obtain information on this connection). It's a wonderful trip.