On online climbing forums, there's calculators to determine the height you have to fall, depending on your weight and movement. Here is one, called "the splat calculator":
https://www.angio.net/personal/climb/speed.html
Unfortunately, going off what I've heard on this website, falling definitely isn't a perfect method. There isn't really a way to maneuver yourself so that you're garunteed to hit your head or neck, and trees, bushes, and other things can break your fall. Worst case scenario, you break your bones or spinal cord, but still remain alive.