This harmonization was also written for the women's schola at my parish, but it could be sung an octave down for a men's schola or possibly split for mixed voices. Verses range from two to four parts. The chant melody and the principal harmony appear throughout the piece and could even be sung alone, producing a simple, two-part rendition of the chant. I took the liberty of elongating one syllable from the chant; otherwise it is the familiar Puer Natus we all know. I hope it may be of use.

https://www.catholicliving.net/puer-natus-in-bethlehem-harmonized/