Sofia's place was perfect for my wife and me during our week-long stay in Paris. Proximity to Metro (Arts et Metiers, Republique) and bus stops made getting around very easy. Walk to great breakfast (Strada Café) and dinner (Breizh Café) but skip The Broken Arm (lots of hype for mediocre experience). We were out and about so much that we mainly used this apartment to leave luggage, shower, and sleep.
Pro-tip: if you need to leave large luggage before the 3pm check-in, consider city-locker.com. The website and emails are a little sketchy, but the actual use of the service was flawless. The closest City Locker is at 82 Rue de Gravilliers, a five-minute walk from the apartment. We used the location at 9 Rue des 2 Gares--only use this if coming in from Gare du Nord; there are a LOT of steps going up to this location from Gare de l'Est.
Also please note--and this is no reflection on Sofia or her apartment--this unit faces into a private courtyard that is used by occupants of several other short-term rental units in the building. You are very much insulated from the sounds of the city but not from voices echoing, metal gates closing, or luggage rattling across the cobblestones. If you are a light sleeper, please consider bringing ear plugs (Sofia even provided a pair!) :)
We will absolutely consider Sofia's place for our next Paris visit.