Hello ajnavickas, and welcome to the forum!
Any of the larger northern towns could easily work since the area is well connected by train. Verona, Padua/Padova, Bologna, Lake Garda and even Venice would work depending on what you are most interested in seeing and doing.
If you post what you are looking for in the place you want to stay people will able to make better suggestions.
I will always go to Venice given the chance but not everyone feels the same way. but if you've never been to Venice then it gets my vote. Verona is very pretty, chic and mostly pedestrian downtown with an intact Roman arena, theater and a cafe culture vibe. Bologna is a university town with an old core and strong emphasis on food in a region with world famous products.
Any of these places will have an easy fast train connection to Milan for your last night.
Hope that helps,
=Tod