We truly recommend Helder's place. It's an apartment with individual rooms with private bathrooms. Our room was clean, with comfy bed and big window overlooking the street (unfortunately quite noisy at night but well, that's inevitable in a big city). We stayed there during extreme heat in Lisbon but the room didn't warm up badly. The shared kitchen was very clean and well equipped. You could even use washing machine free of charge! What is more the location is convenient between Martin Moniz and Intendente metro station. It's on the hill (like most of the city), so be prepared to walk up - a great pastry shop around the corner will make up for it.