Hi Bob

Best plan your trip via Deutsche Bahn, it has up to date schedules and itineraries for most of Europe. Give your search request here: https://www.bahn.com/nl. You can also reserve your seats on German trains their (select "seat reservations only" when you plan).

I think you want to split your journey in two parts? I would advice you travelling over Switzerland. Most trains will have only optional seat reservations then. And you avoid some very expensive seat reservations (like on Thalys) and a cumbersome switch of trains and stations in Paris. 

For the trains to and in Italy, you'll need seat reservations. 

You can get these the easiest via ÖBB (Austrian Railways): https://www.oebb.at/en/. Plan a stretch of your trip (e.g. MILAN- NAPOLI), add a discount in the travellers information (Interrail /Eurail) continue, and you'll see seat reservations for about €10 per seat, per train for high speed trains; €3 for IC's. 

I think there's also a supplement on 1 cross border EC  train from Switzerland to Italy, but others can advice you better on that.