Looking for a long lasting, FLAT messenger bag.

I want one that I can take to work. I’ll be carrying a couple notebooks (not the computers) and whatnot.

The ones I’m looking at online are either designer-brand and very expensive, or have bad reviews because they rip easily, or they just don’t look flat and lightweight to me.

I want one that has a big flap in the front and is flat (that is, not a large width) and lightweight.