https://www.amazon.com/dp/B01N4M5YSY/ref=twister_B075R647W7?_encoding=UTF8&th=1

My first two kids must have been prone because they both had flat heads despite our really trying to avoid it with my son with positioning, babywearing, etc.

Several brands/styles of this seem to have good reviews on amazon, but I don't know whether their kids would have been fine without it anyway.. Thinking I might get one for the carseat/swing/bouncer but go without it at night.