It usually is impossible to fall asleep when a psychedelic is active but as soon as it wears off and all what's left is "afterglow" it usually is easy. 5-MeO-DMT comes up and wears off very quickly (much faster than LSD): 10-30 minutes for a real dose, just some minutes for a small dose. And the effect of 5-MeO-DMT is such a bliss it is natural to slide down right into a dream then (although you don't have to, you won't feel sleepy and fall asleep without a conscious intention).

As for the weed - you just need a strain adequate to what you want of it. If you want a sleep aid look for a CBD-rich and THC-low Indica strain (or just a CBD-only strain - these even are legal in many countries where normal weed isn't). There is a huge selection of weed strains that feel very different. There are strains good for work (energy and concentration), for creativity and thinking, for having fun, for sleeping and for other kinds of activities. I'm sure there is a strain that will shoot you dead-asleep instantly.