My daughter and I stayed for almost 8 days at Francois' fantastic Montmartre apartment. It was an authentic Parisian experience! This meant that we climbed 21 stairs daily from the bottom of the Metro stop to the apartment - quite a workout (which we enjoyed) on some days and sometimes it was exhausting (there is a lift at the Metro, so use it!). We loved being in the middle of Montmartre (the restaurants, the Patisseries, the life), but still lived on a relatively quiet street (we left the windows open at night and only had very limited street noise. It was perfect!
We loved living in Francois' apartment, but be aware that it may feel like you are staying at a friend's apartment (with all the pluses and minuses). Don't expect a perfectly styled and maintained apartment, but Francois made up for it with his well-equipped apartment (washing machine!) and responsiveness and friendliness in all requests and communications.