I worked on a Kindle cover for my niece last week and now we're trying to get together so she can try it for size. Since I don't have a Kindle, I had to rely on measurements she gave me. I made a prototype and then we figured how to tweak it to make it better. I haven't sewn the button for closure on yet.
This is the inside with folded squares to slip the Kindle under.
I looked through my buttons and I like the bone button but it might be too thick and bulky. I'll let my niece decide. We could also use the button I have on the prototype.