First thought was nope nope nope to diy diving helmet, but looks like it would be quick to remove so not too bad. Feels way overengineered if you just wanted to sit in your pool though.

I know snorkels get into problems with depth as your lungs can’t inhale against the pressure. But I am curious how deep that would get you. The dead air in the snorkel is another issue but you can solve that easily with some valves or just exhaling through your nose. Bit impractical to have a very long rigid snorkel but a tube attached to a float could work. Just not sure what the depth limit would be before you can’t fill your lungs anymore. 1m? 5m?