Here are the detail photos of the bag which I just put in my Etsy shop.
This shoulder strap is
length adjustable with this metal parts.
This is how it looks with a longer strap.
It has a shoulder pad with a 5mm thick foam inside.
Very soft on your shoulder.
The side pocket will fit your water bottle.
The pocket closes with this button when you aren't carrying a bottle.
The bag closes with a zipper,
This is the inside of the bag.
The lid closes to this 2 level buttons so you can close it tight when you are not carrying much.
I used a leather for the bottom of the bag.
Two tapes with 2 level buttons extend from front to the back,
and are secured with studs.
At the back of the bag, there is a pocket to fit this standard size carrier frame.
It is positioned by closing the buttons at the bottom.