You can also read the book by Chris Hadfield "An Astronaut's Guide to Life on Earth." It also partly tells about sleep. Writes that you get enough sleep.
It would be interesting to try, right?
In general, you can read about it on the blog of the Italian astronaut Samantha Cristoforetti (for example, here: livejournal.com).
She participated in special experiment: several nights on the ISS slept in a special vest, stuffed with various sensors. This was the test of the hypothesis that changes in cardiac functions cause micro-awakenings, which worsen the quality of sleep in space.
However, according to Samantha herself, the subjective sensations of sleep in zero gravity are the most positive - sleeping without gravity is very comfortable and comfortable.