I have been using this cover for my k3 for almost 2 years now. The magnetic clasp is strong and keeps the cover closed. Also when the cover is open the clasp works in the open position by flexing it backwards. Because I prefer reading in landscape mode, it is perfect. I slip my hand between the covers that are held in place by the strap and read.
This is a k3 cover but I would expect if they or someone else makes one like this one for the paper white it should work the same.
Edit: The strap is the built in magnetic one and not the rubber band shown in the link.
http://www.amazon.com/CrazyOnDigital.../dp/B00428C1I0