I have a laptop bag, but I'm currently looking for a sleeve that I can slip my MacBook into before it goes back into the bag. It'll also be used underneath my laptop (if it's ever on a dirty surface). For the past few months I've been using the (don't laugh!) thin sleeve the Macbooks come with, but this has started breaking. I've looked around at the Apple store etc. but all the sleeves seem too heavy - duty with zips, extra compartments and more. What's the best buy?