what’s a good substitute for coconut milk?

Hmmm...to be honest I don't think there is one in this recipe. The lime coconut combo seems like flavor base here. But you could try another dairy free milk (though I'd suggest making at home so you can make it thicker), yogurt (full fat to decrease the chance of it curdling), heavy cream, sour cream, or a mix of half and half and sour cream.