If you don't mind to stay in a basic hotel that isn't brand new and could spare the extra dime, then Hotel Rubens might be just it for you. We had a not too tiny 4-person room on the 4th floor with bathroom. Both were clean and in an okay shape. The water was warm and stayed warm, which is not always the case when you're a group of four.
The hotel is located in a decent neighbourhood, within walking distance of the Panthéon and the Seine. There are all kinds of restaurants and bars in the area and.
One more thing: don't take the elevator. It's claustrophobic and old. One night, when we got back, someone was stuck in the thing.More