I don't have particular charity recommendations, but for preventing human suffering:

1. Preventing ppl from being born: contraceptives, abortion rights, educating and distributing abortion pills for easy abortions. And educating girls, as that means less children.
2. Viewing life as a right instead of an obligation: Fighting suicide/euthanasia stigma, euthanasia rights, maybe some neater way for DIY euthanasia similar to abortion pills. NOTE: I am definitely AGAINST convincing anyone to end their life. I also think that ppl deserve help for mental suffering, however that help should be optional for them instead of imprisoning in hospital wards etc