Our stay at Jessy's place was amazing. There is nothing I can think of that would improve the our stay there.
For the host: Jessy was very helpful and forthcoming, especially when we realized that our plans had changed a little bit (due to a mix up of dates) - Jessy really went above and beyond to accommodate us, and we really appreciated that! Jessy also has an amazing collection of tips of what to do in Berlin - everything from historic sites, museums, etc. to good restaurants and family activities. We didn't have time to do a lot of research/planning before hand, so this was really helpful!
For the apartment: The layout and size is great and fit us very well (though we were only 2 people). The place was clean and very cozy, it is very well taken care of and has a unique, but well thought out style. It was a joy to spend some time there when it was raining and we wanted to relax in a warm place. The shower works great, the bed was really comfy, and the amenities in the kitchen were plentiful (though we didn't use them). We were able to walk to most of the sights that we were interested in (Reichstag, Brandenburger Tor, Bernauer Strasse, Hackesche Höfe, Museumsinsel, etc.). There's a lot of great restaurants in the area, also within walking distance.
I highly recommend this place if you're looking for a central location that feels cozy and clean.