Technology:Head for Monarchy for Hereditary Rule civic(happiness from units in cities)
As for your overgrown capaital: I would switch off all of that food production. Why do you need any more citizens? Each additional citizen takes up +2 food, +1 unhealthy, +1 unhappy. Instead, I would say you should switch all of the citizens to working cottages and shield-rich spaces.
And that brings up a good point: Why don't you have any cottages around your capital? You have a few plains squares that are just ripe for them. They generate tons of commerce by the end of the game, and makes your capital much more productive. Farms are really great, and I see you put them on a lot of Flood Plains squares. While they are really useful with farms, Flood Plains become gold mines if you build cottages instead.