If you need to be central in Oslo and need something affordable, Aria has a nice little room to stay in!
Aria was very welcoming, communicated promptly, and was very friendly throughout my 2-week stay. It was easy to feel at home, and Aria really does her best to make you feel welcome!
If you're an early sleeper or very sound-sensitive, it can be a bit tougher, since it can be quite noisy in the cafes outside until 23:00-23:30. One day I got unlucky and pizza smells from the pizzeria below wafted into my room for a bit. Otherwise there wasn't anything to complain about for my entire stay.
It was very nice to have a central room to crash, with a comfortable bed, a desk, and a bathroom and kitchen nearby. Aria's great and had good stories to tell over a glass of wine. Happy with my stay!