Need help for itinerary for first Swiss trip

Welcome to the forum! Obvious entrance points when arriving from Paris are Basel and Geneva. You can plan your trips using the timetable. If you don't want to carry your luggage during the entire stay, I suggest you choose one base town, store your luggage in the hotel, and then make day trips. In all, Interlaken might be the best choice if you want to be close to natural beauty and be able to travel to other recommended regions (e.g. the surroundings of Lucerne and Zermatt) within one day. Hotels close to the railway stations are listed here. Day trip suggestions are mentioned here.

I don't know how much luggage you'll be carrying along. If it's too much to travel in a relaxed way, you could consider the SBB Fast Baggage Service for your inbound and outbound trips. This would be especially convenient if you decide to enter via Geneva and travel to the Interlaken region via the scenic Golden Pass line.

Have you considered buying a rail pass? Depending on your plans, a Eurail pass might be convenient. For intensive traveling in Switzerland, one of the Swiss rail passes generally works out better. The Swiss Card for example would provide a free inbound and outbound trip, plus a 50% discount on further traveling. If the idea of free traveling, without having to buy tickets, appeals to you, take a look at the Swiss Saver Pass or Swiss Saver Flexi Pass. These guidelines may help you decide what's best.