New Livy Marie Bag

For her birthday (in March) I told my cousin she could order a customized bag. We finally got around to picking some wonderful Amy Butler fabric and it is ready to go. Before creating it with that fabric, I thought I better do a sample first. Good thing because it needs some tweeking! Here is my sample. I love the look of it and the fabric combination is just right! What do you think Chelle?

I just do not like the way it sags when you carry it on your shoulder. The single strap purses tend to do this and because it is a wide short purse it is even worse. So if my dear sewing mentor who tends to read my blog (aka Trish) can give me some advise I would appreciate it! Do I need a stiffer interface? Do I need to put a hard bottom in it?