Vibrate during the day, ringer on at night automatically

Try a custom ringtone...?

I would recommend creating a custom ringtone that has silence for the first X seconds, then rings however you'd prefer. This would allow you to answer/ignore any calls you feel coming in via vibration, while not making any ring sound for the first X seconds. Then you can leave your phone's ringer on all the time.

The only caveat is that once you hear your ringer, you'll only have 24-X seconds left to answer it.

Feel free to adjust those timings as you see fit, of course.

Alternatively, you could also use a custom ringtone that starts quietly, then gets louder. Same idea, but audible throughout the ring.

Also, a combination of the above could also be employed.

Btw, I believe Garage Band will allow you to make ringtones if you don't have any other options.