Cybrarian

My DGS' s Mom has asked me to make a specific bag for her Mom who has COPD. She has reached the stage where she needs to keep her oxygen on when she is out anywhere. She is reluctant to do this so the hope is that an attractive bag will make this adjustment a little easier. The idea is to have a 2 section bag. The section closest to the body would have a pocket or be only wide enough to hold a single small oxygen canister upright. Then a section-maybe half the size of the first- that would hold mainly a wallet, glasses and keys. I also want to put an outside pocket for a water bottle. I'm all about not reinventing the wheel so if someone can point me to a pattern or picture of something similar I would be very grateful. I will figure something out, I've made several bags, but haven't designed any or needed to make one with such specific needs. It needs to be as compact as possible and I want the length of the straps to make it so her hand can slip under the bottom to take the weight off her shoulder when needed. She is going to measure the circumference and length of the canister and I have to allow for the additional tubing that will need to be stored in the pocket or section where the canister will be. This is probably "clear as mud",sorry, but any help or inspiration is greatly appreciated!