If you progress through a technical program, eventually it'll become an option for you.
If you like deep diving, I recommend reading "A Walk on the Deep Side" by John Kean. It's an enjoyably read about everyone racing to set deep diving records in the 90s and 2000s, and talks a lot about gas mixes and tank configurations and the like. Check out this crazy config, for example, worn by Leigh Cunningham in the Red Sea.