Best train pass for my trip

Hey,

I assume you guys are over 28, so 4 days pass would be 283€. Usually there is Black Friday sale in end of November with discounts of up to 25% (but not always for the 4 day pass!).

and you’d need reservations for Paris-Geneva, Brussels-Paris (or use the slower route here), Visp/Brig to Milano (or take the slower regional trains). So Overall without the sale it could sum up to around  300-350€ per person depending what trains exactly you take etc. 

On the other hand for single tickets you can check on seat61‘s website. He shows the cheapest available fares for Paris-Geneva, Brussels-Paris etc. 

For Geneva to Zermatt you could buy a day saver pass. Bought in advance would be only 52CHF. Then Zermatt to Domodossola the same day saver pass via SBB website. Then regional train to Milano for maybe 10-15€. I guess overall this will be the cheaper option if you book in advance, while Eurail will give you more flexibility.