Hi,
to me, 'Best Hostel Old Town Skeppsbron' is definetly the right choise. It's clean, it's located in the city center (so everything is reachable by walking), the next metro station is 5 minutes away. Unfortunately i can't tell you anything about the public bathrooms, because we had a private bath, but the public toilets were always clean.
I would stay there again!
Greetings from Germany and a lot of fun in Stockholm ;-)
Lars