The mattresses were not great (but not terrible either). The wall with the adjacent apartment is seemingly thin, as we could hear our neighbors well through it. The hotel is a bit far from the old city (20 minutes by foot), but is only 2 minutes away from the train station and has some nice restaurants around it.
We stayed in the 4-person apartment. The apartment was modern and clean, furnished with a nice personal touch of book shelves (in German...), lots of big windows with a nice view and a nice terrace. The bathroom has two sinks (convenient for several people staying together), and there's a large modern cable TV.
Breakfast was good and varied and included fruits, vegetables, a large cheese and meat selection, and lots of muesli, yoghurt, cold and hot drinks. Also hot eggs and another varying hot dish. Price was very reasonable (109 Euro per night for the entire apartment including breakfast for 4 people), and we received a folding baby bed with a mattress and bedding for no additional cost.
Overall, highly recommended as a good budget option.