It depends on your budget, timeframe, and technical inclination.
If you just want to kick the bucket quickly with minimal cost and rudimentary technology, just make an exit bag.
If you want to step up the tech a little without blowing up costs, and you can afford a bit more time to source parts, look into EEBD hoods.
If money is no object, you love tinkering on technical projects, and you have plenty of time to source parts and troubleshoot issues, then SCBA/SCUBA could be for you.