You'll need a global pass.

If, however, these are your only journeys, then buying normal tickets can be cheaper than Interrail plus reservations, so do compare prices first.

Just check: an IR-pass is for at least 4 traveldays-so an ordinary return takes just 2.

BUT; it all depends on your age, where you start/finish in IT and if you are able to still find space on those nighttrains-or if you are flexible enough to use other trains. Or maybe the difference between tickets and pass is so small that you think: hey, nice, I can make another foreign trip for very little (But a pass is only valid on 2 days IN IT for you!!

For normal tickets use bahn.de-though it will likely not show places in IT beyond where their own trains run.