Sebastian and Marcela's place is honestly great. My wife and I stayed there for 3 nights. The apartment is spacious, well equipped with all the necessary stuff (and even more), and extremely well located. We seriously didn't need to buy a single public transport ticket and did everything by walk.
The only two minus points were that: the bed was too soft for us (but its gigantic size helped forget about it) and some of the apartment corners were quite dusty. Beside these two small things, Sebastian and Marcela were extremely reactive on communication, really flexible to organise the key reception and return, and great to provide advises on where to eat and what to visit.
We strongly recommend this place for a short romantic escape to Prague!