If one is going to do this, it is very important to aim as high as feasible, and to get the donations given in an efficient way, which promotes efficient giving. Meta-charity like the Poverty Action Lab, Givewell, etc. Just promoting the idea of giving to charity is pretty likely to result in spending on rich country causes rather than poor country health.

Getting spending on existential risk is more difficult, but a push for efficient charity could perhaps retain that character.