If you look for accommodation in Milan there is no bigger marketplace than the web. You can easily find thousands of accommodations’ offers posted online.
Here it is a list of the most famous websites were landlords, tenants and agencies usually post their offers:
Moreover you can check all Facebook groups and pages were landlords, tenants and agencies usually post their offers.
Finally do not forget to join the group of Milano Easy Renting on Facebook, with lots of posts about flats and rooms.