Let's keep it simple and straight: Helena's apartment is beautiful and perfect for whatever travel you are planning in Lisbon!
It is:
-) Perfectly positioned, for reaching it (300m from a metro station, thus easy from the airport), for visiting Alfama, or for going in other parts of the city.
-) Near to restaurants and monuments.
-) Wonderful internally, with ample and luminous spaces (both sleeping and living rooms), a beautiful sight and all that is needed for a short or long stay in Lisbon. In addition it is full of interesting books (always a plus!) and nicely furnished.
Finally, Helena is super kind and quick to answer!
Overall, this has been one of my best experiences in airb&b and one that I would suggest to anybody, friends or not!!