Great that the O2 is helping you feel much better!
I think you just have to talk to a rep at Rotech. I can only tell you what our experience with Apria has been. They seem to be willing to give us mostly what we want of basic things...regulators, hoses, canulas, washers, etc. But for example, Apria only had one kind of backpack for the small bottles. I've seen different styles of carrying bags online from various websites that we could purchase ourselves.
Apria told us that Medicare would cover the Inogen G3, but if we got that, then they would take away all the bottles. (Well, I think they would leave a tall bottle for emergency, like if the electricity went out and couldn't use the big concentrator.)