I use mostly rolled oats, but depending on your grocery store, there are other "rolled" grains, like rye, wheat, triticale, ect. These are good to mix with rolled oats and give a little more texture.
I mix 2 cups soymilk with 2-3 cups rolled oats/grains and put in a pot over medium low heat.
Keep an eye on it after a few minutes as the soymilk may burn if it gets too hot.
Soymilk or whatever milk, makes it just sweet enough and really creamy. I add a chopped dried fruit and nut mix as well. But keep it too a minimum as it adds a lot of extra calories.