Our stay at Yves-Laurent's apartment in the Marais was great. After discovering that the bed upstairs is much more comfortable than the pull-out couch downstairs we were more comfortable and the stairs to the loft were worth it. The location of the apartment is great--we walked about 2 miles to/from the Louvre and other landmarks each day but there are also plenty of Metro and bus stops blocks away. Yves-Laurent recommended great restaurants nearby as well. The apartment is small--one loveseat and some barstools for sitting but we did not spend that much time lounging in the apartment anyways. There are 4 flights of stairs up to the apartment, a few to the bathroom, and stairs/ladder to the upstairs to be aware of that, also. Yves-Laurent was unavailable to let us into the apartment but communicated well in advance and his friend was able to meet us at the apartment and exchange keys.
Overall, the apartment was in a GREAT location, it had what we needed to set up a home-base in Paris for a week, and the price is fantastic. If you're able to walk up 4 flights of stairs every day then you should stay here.