I got a kindle for my birthday. This was some time ago and I didn't really think I needed a case for it as it seemed quite sturdy and I really didn't want to bulk it up, most of the cases you can get can easily double the size of the indle.
Anyway, the other week I put it in the wrong pouch in my handbag, my key pouch, and it got scratched :( I was gutted as it was my own stupidity that did it but I have been driven to create a case that is suitable for me.
My measurements were kindle width + 1cm x 2and a third kindle lengths. This allows full enclosure and enough for a lovely flap.
Trim the corners from the end you will use as the flap.
Check against your kindle how far you should fold to make your pouch and pin in place.
I used a contrasting embroidery thread but you could use yarn and it would also look good in a similar or tonal colour.
Blanket stitch up one side of the pouch, keep going round the edge of the flap and stitch down the other side.
Stitch on your snap fastener.
If you don't have or want to use a snap fastener just leave it as an open flap and tuck it in for security.
Put in your Kindle and enjoy. Knowing your Kindle will be (new) scratch free.