We enjoyed a lot our weekend at Maria's Majorstuen apartment. It was very stylish and comfy at the same time. The neighborhood had it's own vibe and we felt like locals. We went on foot from there to the Vigeland park and to the center. Maria was very helpful and easy to talk to and the sharebox app we used to get the keys worked like clockwork.
For anyone coming by car to Oslo: we found a small parking lot nearby to park our car for 200 NOK/24h (no time restrictions).