Not sure about going to yr local welder for oxygen.!
For survey ops above 10 k we had a base bottle, and chased up in the field, medical dry breathing oxygen.
See the local hospital
Moisture free for cold lines. And portable bottles.
In Oz it’s above 10, US above 121/2. Skydiving short term to 14.
And Ww1 pilots went to 20k to get above the opposition !