OP, I think the issue here is that you don't know what you don't know. You can drown in a bathtub. I don't know how often this happens, but you can. If you don't know this is possible, you won't have any concern about falling asleep in the bath, which could easily lead to drowning, but if you're aware of this, you make sure to not fall asleep.
You can hurt yourself diving with compressed air in water as shallow as 5ft, half of the deepest you're planning to go for now. So you've figured out that you have to always keep breathing. Great, but what happens if your rig suddenly stops working or you get stuck somehow? Now what?
Dive training is supposed to enlighten you to the dangers you don't know about and how to deal with them. If you really don't want to go this route that many have already suggested, I hope you can at least find a local mentor who knows about these dangers and can help show you the ropes. Everybody here wants you to learn about the dangers and how to keep yourself safe, we just don't want you to learn about them the hard way. Unfortunately the way you seem to be approaching this suggests you're more likely to learn the hard way.
You can hurt yourself diving with compressed air in water as shallow as 5ft, half of the deepest you're planning to go for now. So you've figured out that you have to always keep breathing. Great, but what happens if your rig suddenly stops working or you get stuck somehow? Now what?
Dive training is supposed to enlighten you to the dangers you don't know about and how to deal with them. If you really don't want to go this route that many have already suggested, I hope you can at least find a local mentor who knows about these dangers and can help show you the ropes. Everybody here wants you to learn about the dangers and how to keep yourself safe, we just don't want you to learn about them the hard way. Unfortunately the way you seem to be approaching this suggests you're more likely to learn the hard way.