Konstanz is a popular tourist destination and in the summer it is a particularly buzzing place! It is therefore recommended to book your accommodation as soon as possible.
Some possible options are listed on the University's website, Airbnb, or on Booking.com
Alternatively, Konstanz is home to many "Fehrienwohnungen" (holiday homes), which can be found on this website.
Getting around in Konstanz is very easy as it is a pedestrian and bicycle friendly place, so keep that in mind when booking your accommodation!