I spent a really nice stay in Krystyna studio - the place looks smaller on the picture but actually it was perfect for two people. The sofa bed is really easy to convert and comfy !
Krystyna and her husband Boby were very helpful and provide all information I needed.
The wall are a bit thin so don't expect to have a real silence but I wasn't disturbed since people stopped making noise after midnight.
Moreover the place is located in Montmartre sera and you could reach sacré cœur easily in less than 10 minutes.