We had an amazing stay at Calacatta Housing. It was super close to all of the main attractions in the city, had lots of restaurants around and all the amenities we were looking for. Since we visited in November it was a bit cold but the place had a heater, which was very helpful. The host left a lovely welcome note, some water and cookies.
The apartment is only 5-7 mins walk from the Sao Bento station.
We would recommend the place and stay here again if we ever come back to Porto.