We just spent 4 days in Madrid at Natalia’s apartment. The 2 bedroom apartment with a small sitting area with TV, kitchen, and 4 seat kitchen table was more than sufficient for our family (4), kids 16 and 13.
The apartment is right next to the Legazpi Metro Station serving the 3 and 6 lines (buy one metro card 2.50 and 10 trip ticket for 12.20, a great deal. The card can be used for multiple people). The area is not filled with tourists so you’ll get a slice of life in Madrid. Grocery stores, cafes, bars, and restaurants all nearby.
We highly recommend Natalia’s apartment.