Need an additional resource type for a custom game

The standard way of doing this and the easiest way is to have a store and you buy w/e you need with kings. And you earn more kings how ever you want.

This method works fine but has 2 issues. First it messes with your pop space which can be annoying depending on the game you are making. Also you need to have a very over sized store for it to work. You need to be able to fit multiple kings on specific tiles. Which is kind of annoying.

I'm looking for other ways of having an additional resource that would work better if there are better ways to do it. I assume there are. The king method seems to just be the easiest.