Hey, I have good news for traveles to/in Italy. It is possible to book Interrail Reservations via ÖBB App or tickets.oebb.at (like Freccie 10€, IC 3€), without additional booking fee like via interrail.eu, eurail.eu or italiarail.com.
I haven't try to book it yet but I can go till the paying site.
Note: The reservation has to be printed on paper at home or collected at ÖBB Ticket Offices or ÖBB Ticket machines.