Hello, you can try via tickets.oebb.at choose one passenger and discount “Interrail/Eurail”. 

Maybe you have to book the train from Switzerland to Italy and the second train to Firenze separately. 

The reservation fee is Eurocity 2nd class 11€ and Frecciarossa 10€.

This is a new possibility, please give us a feedback about booking via ÖBB reservations for Italian trains. 

Hi Angelo,

Thank you for your response.

When trying to book the train from milano to firenze via OBB when going into June the train ride suddenly becoms over 1day and 9 hours. 

Is this normal due new train schedules being added as time progresses?

Yes, there is a timetable change in June.

Trenitalia starts to sell some trains of the new timetable (you can check it via trenitalia.com), but it takes some days to get this new timetabel to all other railways like ÖBB.

Trenitalia have just published their summer timetable (long distance trains only for now), starting on 12 June. It will take a few days until that is included in the other planners. Updates are usually early Tuesday and Friday.