7 days in Interlaken, train from Milan?

You will want the Eurocity 52, a non-stop Milano to Spiez. In Spiez, you change to a Swiss train to Interlaken. Go to Interlaken Ost if you are going up the valley to Lauterbrunnen or beyond.

Will you do a lot of hiking? If so, you might do well to move up the valley as Interlaken is rather unremarkable and the true scenery is 20 minutes further on. The passes have been discussed a lot. The Berner Oberland Regional Pass makes a lot of sense for long stays as you get trains and lifts throughout a large geography.

Which train website did you pull this information from?
I am confused as there is an italian train website as well as an SBB website...
I haven't travelled overseas for years; feeling a bit overwhelmed.
Doing a 2-week walking tour of the Franciscan trail in May with a group where leader did background work...
Then hubby said he wanted to see Switzerland, so I am frantically trying to figure stuff out.

My husband and I have to balance hiking, as hiking every day will make him cranky! ;0)
We will take a few day trips from Interlaken, then balance with hiking and sightseeing, biking, or just being part of the people.
Thanks so much for your help!
Tina.

I used www.trenitalia.com because you are traveling fromItaly to Switzerland. Note there are several options requiring a change of trains. I like the direct train. It is a very nice train.

One of the best rail websites for researching travel all over Europe is the Bahn.de (German Rail) website. I normally choose trains based on the travel time and number of changes.

Are you planning to stay in Interlaken? Most of the group here really enjoys the Lauterbrunnen Valley and the communities of Lauterbrunnen, Mürren, etc. It's only about 20 minutes past Interlaken.

If you plan on using any of the mountain lifts (Schilthorn, etc.), one of the Swiss passes such as the Half Fare card may save you some money. Switzerland can be expensive, so be sure to budget accordingly.

Do not use the Italian rail sites to search for train from Milan to Interlaken. They do not show Swiss internal trains, which are required for the last leg to Interlaken.
Instead use the Swiss Rail site: https://www.sbb.ch/en/
and do a search from Milano Centrale to Interlaken (Ost or West), with date and time. here is no fast or slow train option on this route. It will take about 3½ hours.

Are you actually going to Interlaken, or somewhere further up into the hills (Wengen etc.)? If yes, search for MIlano Centrale to your actual destination.