My stay at Denis's place surpassed all expectations. I was traveling with a friend from university, and Denis's flat had both a double bed and a couch with a mattress on it which worked perfectly for the two of us sleeping in separate beds. Both beds were comfortable, and the larger bed would certainly fit two comfortably. His apartment is right in the Latin Quarter, and we were able to walk to Notre Dame, Ile San Louis, and other spots in less than 20 minutes -- probably 15. For a big city like Paris, these destinations are practically in Denis's back yard. His flat is also 15 minutes walking distance to the San-Michel-Notre-Dame train station, which connects with the airport and other parts of the city. This was very convenient.
Denis went above and beyond in his hospitality. Before us arriving, Denis sent us a whole list of things we could do, places to eat, etc. We did not meet in person, but he arranged for us to easily pick up the key from a nearby restaurant (a 2 minute walk from the train stop). Entering the apartment, we found a note from Denis welcoming us to his home. He left us maps, a couple metro tickets, and a bottle of wine. It was truly a treat.
The only, really the only, part of our stay in Paris that wasn't amazing was the hike up to Denis's flat on the top floor (8 stories). I do not believe there was a lift. But for those who do not have accessibility issues, the view from his flat is worth the climb. You can easily see Notre Dame, as well as a huge swath of Paris, including the beautiful Sacre Cœur in the distance. At times we were able to see the top of the Eiffel tower, especially at night when its search light shone out over the city.
You really can't beat Denis's place. We would stay there again in a heartbeat.