1mg is a good starter and nothing higher than 2.5mg or so. I think melatonin actually has a lot of other health benefits too, since it helps regulate hormones and has (good) antibiotic effects. It’s been shown to be completely safe even in doses up to 400mg, so toxicity isn’t an issue. I was reading about it just the other day. Making sure you’re not in ketosis might help you sleep too. You can tell pretty easily if your pee smells bad.