Cannabis does not need a super humid environment, it did not evolve in tropical rain forests. Save your money and keep your humidity lower, especially during flowering, otherwise fungus and mould will become rampant. Apart from trying to prop your plant up, you could always add some more substrate to your pot so that half of the stem is buried and this will support your plant. Over time the buried portion of stem will sprout roots and this process will not harm your plant. Hope this helps,.. Organoman.