Hi Saul <3
I use to have that problem - I'm Colombian so drinking coffee for me is second nature (Actually, it WAS second nature as I quit drinking coffee)
What I use to do (Or rather, still do) is use strawberries and baking soda. After brushing my teeth with this awesome toothpaste:
I'll cut up a strawberry in half, put some baking soda in it and rub it all over my teeth for a good five minutes. After, I'll brush it all off with a tiny amount of toothpaste to get rid of all the strawberryness.
Followed by this awesome mouthwash:
Or you can make your own hot water and salt mouthwash.
I found that this has worked perfectly for me. It's natural and very inexpensive. Also, only do the strawberry thing ONCE a week as doing it too often can damage your enamel~
Hope this works for yoooouuu~ :3