I had a great time at David's Boat.
Don't expect luxury or high standards - this is just a small cabin with a 1,40m bed. Best for singles or young couples. It was super cozy, clean and comfortable. I had a great sleep there!
The boat is around 2km from the center. Right around a corner you'll find everything you need - the tram station (a few minutes to central Station), Cafés, grocery shops, coffeeshops, etc.
In a 15min walk you can reach the zoo.
David was super friendly and a really nice host, and I'd love to come back!