I recommend this Airbnb. We stayed there during the Porto days in our Portugal trip. The good thing is if you have a couple of days in Porto, you easily can go one day into the city center and on the other day to the local beaches (both ways take like 30-40min of walk (or you take the bus).
All in all, Sergio is really friendly, supportive person, who helps you with any questions or provides some really good recommendations.