A messenger bag is a very poor choice for a school/ book bag. Get a backpack 2 straps.

If you insist on getting a Chrome bag, get their bravo. It is designed to be a bookbag for school from the get-go and is definitely one of their underrated bags.
If you can hold out for another half year, they're releasing a barrage pocket backpack which is a cross-over between their bravo and barrage bags to provide the benefits of both cargo capacity and book-bag accessibility.
The mini-metro was actually designed for women to fit their smaller frames. The citizen will fit a 5'6" person very nicely.

Protip: if you even think about carrying your laptop/ tablet in any chrome messenger bag, get a padded sleeve for it!
Their messenger bags have no padding whatsoever aside from the strap.

Also, never pay full price for a Chrome bag. They always have sales where you can stack on additional discounts from their email sign-up coupon.