Can anyone help me find a modern day song that includes plainchant?

You should have a look at the Wikipedia page for Gregorian Chant. In the “Twentieth Century” section, they list bands like Enigma and Iced Earth, who use plainchant in some of their songs.

@dappled_leaves, thank you! I will do just that.

Gregorian are a German band that cover pop songs in the style of a gregorian chant. It’s as weird as it sounds.

Yeah, I was gonna suggest Enigma’s first album. along with Chill Out no chanting on Chill Out come to think about it but just I use them for the same reason, too fucked to sleep need auditory help.

Adult Lullaby’s