These are the essential oils I use. I mainly stick with Cassia Bark. It's a cinnamon-y scent that smells clean and sort of spicy.
I found mine at our country health food store. I live in a SMALL town and managed to find them so you should have no problem ;)
Oh, and I just keep a printed copy of the instructions taped on the inside of my cabinet under the kitchen sink so I never have to go looking for it when I'm running low.