Cascara sagara seems to be a big favorite. Oxypowder
helps a lot of people, though some find that too many days of use can be draining physically. Some not.
Just eating a couple of big tubs of air popped organic popcorn can have a laxative effective and maybe in the most natural way of all. Put on some Seasalt
, cinnamon or some other spice & just a touch of butter or coconut oil (or even no fats at all) & enjoy!