Do not Disturb is wonderful; I use my phone for sleep tracking (particularly essential in my case) as well as an alarm clock, so just turning it off at “night” isn’t functional for me.
However, also had non-zero amounts of anxiety about people needing to urgently contact me. Didn’t find a particularly satisfying solution for a while, until I changed phones and came upon the “ring if same number calls a second time within 15 minutes” mode. A simple solution; also, obviously, if you *really* need to get ahold of me, call a second time. (I’m more than happy to get woken up to help out someone really in need, or otherwise bail out a friend)
I know its existed for a while, and might be almost universal at this point, but its also amazing and I highly suggest everyone use it who wants to be available for emergencies but otherwise not have a phone around (or download an app that does it).