You can start by trying to get an O2 prescription from a doctor and then having it filled by an oxygen supply company, or you can set up a system using welding oxygen. If the first route is straightforward and affordable, it's probably the sensible way to go (if you have a competent doctor who will prescribe O2; and if you have insurance to pay for the doctor visit and the O2, or you can pay out of pocket for those things), but welding is simpler and ultimately no more expensive, particularly since you are probably going to pay for a higher-lpm regulator even if you get one from the medical O2 supplier. Welding O2 is discussed here: https://clusterbusters.org/forums/topic/5627-notes-about-welding-o2/ There's a lot about O2 here, plus some things aside from O2 that might help you until you get O2: https://clusterbusters.org/forums/topic/6213-basic-non-busting-information/