If you can breathe, so can your yeast.
When I siphon from the kettle to the carboy, I clip the tube to the side of the fermenter so that the wort runs down the side. That means that every drop of wort is exposed to oxygen for a little while. That's all the oxygen I've ever needed - if you're worried about altitude, try adding that technique to your process, and then shake as well. That way, oxygenation becomes a two step process and you'll be assured that you've got enough.