Hello Chouyalai66
Good day …
You can choose your seats when booking through Trenitalia during the ticket booking process. Simply activate the ‘select seat’ option after having selected the offer.
There is no issue when booking with TI, the ticket is either valid since the train is jointly operated by SBB and TI.
But: it is not a high speed train; it is simply a border crossing train. And, we call it 1st class or prima classe, not business class.
Kind regards,
Roland
