We spent a very good time in Paris also thanks to Matthias who was very halpful in many things although we never met him. (ex. Thanks to him, we didn´t have to wait in queue in Louvre, we went directly to the museum. THANK YOU! :D )
His apartement is small but very nice and cosy just like in pictures. There is only one thing that mattered us little bit - the smell of solvent (only in the flat hall not in the apartement) because of the reconstruction of the whole flat, but this is not Matthias fault. It was good that whan workers started working (in the morning), we always went to visit the city and whan we returned in the evening, workers just ended their work. (They were also so kind.)
The surrounding is great, lots of bakeries and also a supermarkets in near streets. Sacre Coeur is about 10min away from the apartement and the metro station Marcadet-Poissonniers is really close too.
We recommend Matthias's apartment to everyone who wants to spend beautiful moments in Paris. Just prepare your legs because it is in the last floor (6th) but the apartement is beautiful so you will enjoy every moments in it and in Paris as well.

ps: Again thank you for the map and two tickets on the metro. ;)