Hello Vaesse...
I have a
Kensington Simple Sleeve.
No magnetic closure, but it does not need one.
The link I have posted is Kensington's own, but if you shop around you can find these for more like $10. I did.
It is not at all bulky, and the Kindle (up to Paperwhite in size) is a snug fit, and well protected. It will not slip out of the sleeve, and nothing is going to scratch the Kindle either.