Hallo Sarah I am glad you join the bag makers and users. I like your pattern with the wide side panel. if i may, can i share some of my many years of bags` sewing and using experience.
Bags can be made from Any strong cloth. Even strechables can be used if theye are lined. I like to line bags = sew the bag twice , either from same or different cloth, the lined ones , have lasted longer.
Bags that are intended to be folded into your purse, i make from rather plain cottons, They don`t complain when pushed and squaeezed into my purse.
It is a wonderful feeling to use some inner cloth, and than crazy quilt [with sewing machine] all kinds of leftovers from your older sewing projects.
Old male shirts, make for good linings.
Do try the wanted Length of your shoulder straps.
I also made some smaller bags, for the Content of bags [ purse] , i keep my little callenar, check book in one tiny cloth bag, tissues in another , the cord of the cellular in another , This way they are better kept, and are easy to pick out when you need them and easy to be remooved from bag to bag. mirjam