Try eating a few prunes (soaked in warm water first) before bed.

For supplements try: Triphala ("three fruits"-an ayervedic product)
or collinsonia root. Both are not laxatives.

Smooth Moves tea is an excellent gentle tea to get things
moving-although it is a laxative (has senna), while the above things
aren't. Sometimes there's constipation only in the transition stage,
and a cup of Smooth Moves before bedtime for a few days can get things
going.

Laura