Mathilde's apartment is fantastic and provides great value. The apartment is located in the Latin Quarter which is a neighborhood that is lively, diverse, walkable and bursting with life.
We stayed here with five adults and four children under the age of 5. We had no concerns with stairs as each floor has a door effectively creating three separate apartments within the house.
We did not find the noise to be distracting - it was in fact charming as you could hear street music and people enjoying their night. Being located on top of a square is extremely convenient to purchase meals, groceries or get anything else you want - everything is within one or two blocks. The Pantheon is a five minute walk away and Notre Dame is a 10 or 15 minute walk. Access to the rest of Paris is very easy. We stayed during the last/first week of July/August and temperature was not an issue.
Mathilde's property comes highly recommended!