I completely agree with all the positive reviews people have given to Mathilde and Jean-Pierre. Simply put, they were great hosts. They helped us with laundry, provided options for us to store our baggage after checkout, provided some nice snacks and provided excellent recommendations for local eating establishments and attractions.
The apartment sets on the fifth floor of a building in an excellent location with many restaurants, bakeries, a great grocery store all within a block or two. It is a fun neighborhood to simply walk around in and explore. It is lively and feels very safe. There is a bus stop out the front door and at least two metro station within a few blocks as well. It is within walking distance of the Louvre, the Basilique du Sacré-Coeurthe, the Gare du Nord train station and many other attractions.
The apartment faces a courtyard, so it is quiet. It is spacious enough for a family of four, beds were comfortable and it was very clean. In other reviews people have mentioned the shower as it is built under the stair well - it is definitely unique in a good way, and worked very well for us. We would definitely recommend Mathilde and Jean Pierre's place to anyone planning a stay in Paris.