The first time I’ve ever stay on a hotel ship was the Hotelschip Gandalf in the city center of Amsterdam. The ship is located in a great location and close to many attractions, like the Heineken Experience, Anne Frank Museum, or the Red Light District. To my surprise, I was not able to feel any movement of the ship- this was a relief considering I get serious motion sickness.
Each night was around €80. The rooms were small and dated.
Side Note: Free wifi and breakfast