Hello Haucouwhou21
Welcome to the SBB Community and welcome back to Switzerland.
I think, nobody answered your question yet because nobody wanted to speak out loud their opinion š¤Ŗ
Despite the fact that Swiss do no like to talk about money (you might remember that), the saying āmuch cheaper than Switzerlandā against a Swiss is rather a faux pas. We do not like these comparisons, although there is certain truth š
In your case, however, I, personally, think that you took a totally wrong decision. No, you are not a dumb, but your decision is not wise either. Diessenhofen is nowhere near the Swiss Alps, nor centrally located, allowing you to get āhere and thereā easily and quickly. Surely, you will spend a lot of time for ācommutingā. Perhaps, yes, you will see savings from a money perspective but definitely not from a time perspective. It will not mean easy travel; you will face long travel days if your places of interest are not all around Bodensee. And, I think, this should weigh in on your decision at your age.
Please check again the travel times using www.sbb.ch/en. A place like Bern or Lucerne would have meant a perfect home for your last visit.
As I said, this is my opinion, yours is different. I only wanted to share another point of view although your question was ticket related.
What concerns the travel cost, no matter where you will be staying: I suggest getting the Swiss Half Fare Card plus single tickets or the GA Monatskarte. The latter gives you full flexibility and allows you using the Swiss public transit network at will. You can get it at the ticket office upon arrival.
https://www.sbb.ch/en/tickets-offers/travelcards/ga-travelcard/ga-1-month.html
Viele Grüsse
Roland