I had a pretty cozy stay (haven't slept so good in a long time - very quite, comfy bed) in a room on the second floor at Conscious Hotel (The Tire Station), which is at the south-west end of the Vondel Park. (around 15-20 mins walk from Leidseplein).
Check-in / Check-out: Pretty smooth self check-in through Ipad minis
If you have questions throughout the day, you'll always find someone from the staff downstairs near the elevators.
Since the check-out time wasn't near my flight, I postponed it via the link provided by mail. Additionally, I check it with the staff at the counter.
All in all, pretty smooth experience. I can recommend. :-)