We had a fantastic time at Susana's apartment. It is incredibly close to the Castle and Alfama and then about a 25 min walk to Barrio Alto.
The apartment is really light and spacious and was incredibly clean and I would really recommend it.
The only thing to bear in mind (although not an issue for us at all) is that the stairs up to the apartment are incredibly steep so may be a little tough for some people.
If you get a chance to stay here then you should.