Emilia and I had a great stay in Isabel's apartment. She welcomed us when we arrived in Porto and gave some good tip. She was also very flexible about check in and check out. In the apartment everything was so tidy and clean, the bed was comfortable and most of the nights were very quiet (of course sometimes you can hear people talking down the street but it's not so annoying). The position is perfect, near the Douro river, and close to the city center as well.
What to say about the city of Porto? It's very nice, relaxing and charming! A little cold maybe, take some Autumn clothes with you! :D