Using a zipper to close a bag is as easy as it gets. It only comes in one colour, black, but it does look quite neat.
From Joom
Dicota D31102 Black 13.3 Laptop Sleeve TU transparent
Technoworld PLC
Dicota Ultra Skin Plus PRO notebook case 33.8 cm (13.3") Briefcase Black
This product is also available at 4 unverified stores.