We visited on early December and the temperature was perfect. If it got somewhat chilly, there are multiple heaters that kept us warm as well as a selection of blankets. Cozying up next to the beautiful dormer windows while listening to the rain on the roof above you is quite the magical experience. The apartment is truly charming.
It was great staying at Helena's, she's a wonderful host. She checked us in personally, had wonderful recommendations and arranged for some basic supplies to get us started. She made us feel right at home and was very responsive to any questions we had.
The location is great for a quiet and peaceful stay, with the Basilica bells chiming once in a while. The iconic E28 tram goes right by and will take you to the city center (PS, Uber is also very affordable in Lisbon). We worked remotely in the apartment for part of our stay, there's very good internet connection.
Overall, highly recommended. Helena is great and this apartment is wonderful.