Accomodations in Barcelona and Madrid

We are going to Barcelona and Madrid at the end of May. Will spend about 3-4 nights in Madrid and 5-6 in Barcelona. Looking for suggestions small/boutique hotels (besides VRBO and booking.com) to stay in central location in both cities. We love to walk, take metro; don't need luxury accommodations and will not be doing any cooking. We are a married couple in our 50s who love good music, food and are interested in nice places to stay up to $300 per night.