We have been to Paris a few times and just love the area that Sarah and Dimitris apartment is in. It's walking distance to most of the major attractions, and plenty of great cafes and bistros. There are also a couple of supermarches close by.
It's worth mentioning that the stairs can be a little awkward to navigate with large suitcases. However, all in all, it was a great stay in Paris.
If you are a coffee afficionado then I would recommend Lapey Ronie, close to the Pompidou. And there is a gym, Cercles de la forme, also next to the Pompidou, that you can get a one week membership for.