Thanks for your hospitality Iwona, and Jastin!
Iwona was very thoughtful and very responsive, always asking if everything is alright. She made sure to communicate with me clearly and ahead of time about check-in and check-out, how to get there, etc...
Iwona's place is really great: very cute and clean, very sunny (may get hot but there's the AC), ideal for 2 persons. There's everything you need there. It's close to the center, the streets are very quiet. If you're coming by car keep in mind that the zone is restricted to authorized persons only so you need to find a parking space close-by.
Would definitely book again if I come back to Madrid!