We stayed 4 nights at Sandra's place. It's very well located, right next to the metro and only a 15-20 minute walk from the centre, with lots of local shops around. The house is a lovely 1920s building, very tastefully decorated and with good kitchen facilities. The room itself is not very big, but suited our needs. The bed was comfortable and there was a little balcony where we sat in the evenings.
Sandra was a great host, extremely welcoming and helpful. On the last day we had an evening flight and she let us leave our bags with her while we did a final walk around Porto. I definitely recommend this place!