With two of my friends, we really enjoyed staying at Arantxa's for over a month. Madrid is a great city to live in, even though it was starting to be a bit hot by the end of May (at least for French people like us).
The apartment is located in a great neighborhood (very quiet, with a beautiful view and near transportation services), and is equipped with everything you'd need on a daily basis and more (dishwasher, washing machine, microwave, oven, blender, coffee maker, kettle, plenty of cutlery, vacuum cleaner, TV, WiFi, etc.)
You also have free access to a great fitness room (well equipped, with only a few people in the afternoon), a sauna and a swimming pool (that we unfortunately couldn't enjoy as it opens only from June).
The location can seem a bit far from the center of Madrid, but you can easily take the metro (5 min by foot from Puerta del Angel, 10 min from Principe Pio) or different buses (at Principe Pio or Puente de Segovia), or even go by foot (only 20 min from the Palacio Real for instance).
Arantxa has been a kind host, always available when we needed information or anything else. Thank you !