Paris to Switzerland to Dolomites

You can get from Paris to anywhere in Switzerland by train and/or public transit. Use www.sbb.ch which can plan your trip, and sell your tickets, to pretty much any public transit stop.

You can travel from anywhere in Switzerland to anywhere in Italy again by train, and the same website, www,sbb.ch will again show you routes. You do not need to make any a priority assumptions on what the route will be, and you start the journey wherever it is that you need to start it...
(For me every train trip starts at the station of Wengwald, regardless of where the trip goes to for example...)

The mountain villages are of course nicer than Interlaken, but maybe for you the Youth Hostel in Interlaken (which is very nice, and which also has rooms, not just dorms) could be a good option.

Where do you plan to go to next after the Jungfrau area? Can you be more specific than "dolomites". Because there may indeed be some interesting scenic options.

Thank you very much for your reply.

I did not plan to go anywhere else in Switzerland outside the Jungfrau area as I thought it might not be enough to do much else as I only have 3 days there. Unless you recommended somewhere else?

I will be doing the Alta Via 1 and I will be staying at Lago Di Braies.

Staying in the valley i.e. Lauterbrunnen provides convenient access by cable car, gondolas, mountain trains or lifts to Murren, the Schilthorn, Mannlichen and Jungfrau. While Interlaken is okay staying there would add another 25 minutes trip by train just to get to the valley. The other areas that you mentioned sound wonderful and may also be convenient but I can’t provide recommendations since I’ve only visited each once during a day trip. Nonetheless these areas are beautiful.

To get from Lauterbrunnen to Villabass/Niederdor you are probably best of going via Innsbruck, and booking with the Austrian railways here: www.oebb.at

That is going to be. a long trip, but it is a nice scenic ride.