Use baking soda daily to whiten your teeth. It tastes terrible at first, but you get used to it. Just wet your toothbrush and dip it into the baking soda and brush as usual. You also need to follow-up brushing with regular toothpaste for flouride, etc., and also the minty taste will get rid of the baking soda taste!
It works and I’m a tea drinker, so my teeth were terribly yellow, and aside from professional whitening (which made my teeth very sensitive), nothing worked very well & I was spending a lot of money on various products.
I did check with my dentist’s office, and there is no problem whatsoever doing this, as long as you also brush with regular toothpaste. This is what people used to brush their teeth before toothpaste was invented!