I can't imagine a better location. You are right in the very center of old town, with easy access to all of the main sites. What's amazing is that on top of that, the apartment in in a 500 year old building with very thick walls and the moment you go through the door, all of the touristic craziness fades away. Quiet day and night. When I was exhausted and sick of people, I ordered food from Au Gourmand, 2 minutes away, and ate in the sitting area of my home. And, I was able to save leftovers in the fridge so that I had snacks for my early starts.
So that's about the great apartment. Jan, is a super super host (I know what work it takes as I am one, too). When he picked me up at the airport, I had just realized that I left my passport on the plane. He tried to help me find a way to get back to the plane, but they assured him that the cleaners would find it and I would get it that night. They didn't find it, (he did all of the calling) but he assured me that I would be OK and the embassy would give me a new one and he helped me with the logistics. It was a weekend, so I couldn't do anything until Monday, but the US embassy was only a 20 minute walk and after a 15 minute visit, they told me to come back in a few hours and it would be ready and it was. Jan is a very dear man who really takes his role as host seriously. Stop looking at other options and book with Jan! (I bet Sarah is great, too, but I only met Jan.)