I'd suggest a tiny pinch (<0.05g) of dry herb in a vaporizer, a couple hours before bedtime. Recurring costs are <$20/month in a legal state.

The immediate effect is quite interesting: routine tasks become less-accessible while imagination becomes more-accessible, so you think more about what you're doing, which often spawns new ideas (e.g. the desire to exercise or play an instrument, understanding both as a cyclical muscle control problem.) Afterward, the transition to sleep feels trivial.

Large doses are generally not beneficial.