Start here:

• Global poverty and the demands of morality (Toby Ord)
• Growth and the case against randomista development (Halstead and Hillebrandt, 2020)
• Cause profile: mental health (Michael Plant, 2019)

Further reading:

• Famine, affluence and morality (Peter Singer)
• "Why Nations Fail" and the longtermist view of global poverty (Ben Kuhn)
• A taxonomy of happiness interventions (Michael Plant)
• Exploring hedonic adaptation and its implications for happiness maximisation (Michael Plant)
• What should a billionaire do to maximise human happiness? (Michael Plant)
• The price of glee in China (Scott Alexander)
• Cash transfers are not necessarily wealth transfers (Ben Hoffman)
• The moral imperative towards cost-effectiveness in global health