Amazing location, right in the heart of Barcelona. Mercedes is an excellent and generous host not just offering a solid B&B experience but also unexpected extra's, like a portable wifi-hotspot.
If mobility is an issue, keep in mind you'll be walking up and down some five, six flights of (broad) stairs. Also, the area is very lively, even in February, so it will never be completely silent. That said, noise was never an issue; I had no problems falling asleep.
Recommended!