I had a great stay at Heidi's apartment! The place is very cozy, and the building has easy and quick access to public transport. It is a bit far from downtown but it offers a perfect opportunity for some hiking in the nearby woods+lake (besides the train to the center takes only a few minutes).
Heidi was very kind and attentive, welcoming me warmly and providing all the help I needed, making me feel at home.
I loved my stay in Oslo, and recommend this option for any travellers :)