Supplemental oxygen - portable options

I am starting a separate topic for supplemental oxygen to have in one place to avoid searching multiple discussions since no matter the cause, the equipment is the same.
I am interested in any information, experience, suggestions people can offer about oxygen tanks/cylinders.
I have pulmonary fibrosis and for two and a half years I used an Inogen Rov 6 portable oxygen concentrator. While it has six settings it is pulse rate and not the same as continuous flow. My prescription was for 2 liters continuous flow for exertion and sleep, Now my prescription has increased to 4 liters continuous flow, so the Inogen will not meet this need. My O2 provider is bringing me tanks of different sizes to try out, and I am told they come with a regulator to conserve O2. Obviously when one gets low, one can't charge it like my Inogen! Thanks for your help