Danhiel Thanks, but this site only links to Bernina and Glacier Express. And yes, there you can choose the exact seats you want. But that’s not the case for the other Swiss trains, like the regional trains from Zurich to Chur and from Brig to Luzern via Bern.
And I realise that you can sit everywhere, but esp. the Zurich to Chur train can be very busy end of the afternoon. And with 2 suitcases we don’t want the hassel of having to search for empty seats and then not finding them.