Marc Jacob makes some real cute simple bags just for carrying MacBooks and you can find them online or at Nordstrom.
Also: I just realized this was a dumb answer. I use a backpack for going to class or a leather tote bag so I don’t really know how to help you out. If you’re looking for something simple that will last a long time I would go for something high quality like a Fossil cross body bag. If you’re looking for something trendy and cute I’d try Asos, Topshop or Zara