Julia’s loft is a great solution if you want to visit Gaia and Porto. Very well positioned, just 10 minutes far from the metro station by foot. The line (D) goes directly to Porto (Jardim do Morro for a great view on the sunset from Gaia or São Bento if you want do get off at the city of Porto).
The loft is very clean, with all the services you would need to feel at home, even a nice garden to relax.
You can have a fantastic breakfast (included in your staying) into the padaria, just crossing the street.