You need to make some calculations yourself as there are many factors involved!

Where in Italy, which date, how many people, etc.

In my opinion the best option is advance tickets for Italian high-speed trains and half-fare card + half-fare point-to-point tickets within Switzerland. The 50% discount also applies to Jungfraujoch so it is very interesting.

It'll require some planning though as advance tickets for high-speed trains are cheaper the earlier you buy them. Trains rarely sell out so if you don't mind the extra price you can get them closer to travel.

Read these links about Eurail too (esp. on mandatory reservations) :

https://www.seat61.com/how-to-use-a-eurail-pass.htm

https://www.seat61.com/interrail-and-eurail-reservations.htm

Feel free to come back with more specific questions.