First of all, the TGV from Paris to Switzerland is ridiculously overpriced when reserving a seat via interrail.
Only take the TGV until Mulhouse (Fr) and switch to a half-hourly regional train to Basel (no seat reservatoin possible). It’ll cut down reservation cost a lot and barely costs more time.
Book your seats Paris-Mulhouse here: https://travel.b-europe.com/Eurail-GE/en/booking-tgv#TravelWish
You can select your seat preferences there, but not choose from a map.
For which you’ll need a pass cover number:
When do you want to take this train?
For Italy, when you’ll book it via the interrail reservation service, or the ÖBB website, you’ll have the same issue of not being able to select your seat.