Peter,

cannulas are a much more comfortable solution in that altitude. You
should get an oxymeter to check your blood oxygen content, too. Are you
familiar with www.aeromedix.com?

Also, don't know about rules in Europe, but in the US it is perfectly
legal to fill the bottles yourself from welder'S oxygen bottles. It is
the same oxygen anyway. Check for some columns at www.avweb.com on that
topic.

--
Thomas Borchert (EDDH)