I recently attended an event at this place:
http://www.pestana.com/en/hotel/pousada-lisboa
It opened in September 2015. It is in a renovated historic building (I think a former government building/ministry), right on the main square. Not sure if this is really a luxury hotel as I did not stay, but public areas were very nicely done, and the location is perfect. In any case, would provide more sense of place than the 1970s concrete box FS.