Basis in Switzerland

This is my first post on any forum. Hope it works!
My wife and me will be travelling in Europe when I retire next year. We plan on going for 3 months (schengen visa limit). We are South Africans. We plan to travel by hired camper and visit several countries.
We plan to visit Switzerland for 5 or 6 days during May. We did travel by car to Grindelwald about 5 years ago. It was just a short visit and want to go back!
Now for my questions.
1. We want to stay the 6/7 nights in a basecamp and use at least four days to travel from and return to this basecamp by train for the views. Which city/town will be the best for such a basecamp? Sights in the town itself will be of low importance.
2, Which routes do you recommend? I believe the Jungfraujoch is a must. But that is one day! (We will get swiss passes for the four days.)
3. The 5th day will be spent in Bern as my wife is an artist and would like to see the Paul Klee museum.

Any information will be welcome.

Hello Denita, welcome here! I can imagine you want to return to Switzerland after your short stay in Grindelwald :-). As for your questions:

1) Assuming that you want to return to the Grindelwald region (in the Bernese Oberland), centrally located towns would be Interlaken and Spiez along the shore of lake Thun. Interlaken gives good access to the Jungfrau region and has camping sites in and around the town, whereas Spiez also offers direct connections to Thun, Bern and Brig in the canton Wallis. Both towns are only 20 minutes apart by train, so there isn't a major difference in traveling times. You can plan your trips using the online timetable.

2) A visit to the Jungfraujoch is indeed an exciting and beautiful day trip. The same goes for the Schilthorn, which has spectacular views of the Bernese Alps. Other trips I'd recommend (again, assuming that you will mainly discover the Bernese Oberland) are boat trips on lake Thun and/or lake Brienz and a cog railway ride up to Schynige Platte or Brienzer Rothorn.

I hope your first forum experience turns out to be a good one!

Than you modanika. I will study the maps and the time tables. Will come back if need more information.