Did you know you don't actually need toothpaste to keep your mouth and teeth clean? It's generally the brushing action rather than the lather created by toothpaste that keeps your teeth and gums healthy. In fact, your mouth will probably be healthier if you flossed regularly without brushing, than if you brushed regularly without flossing.
When you think about it, if you are already maintaining proper oral hygiene by regularly cleansing your mouth of food debris and bacteria, there is no reason why you should need to add chemical-laden toothpaste to the mix. Moreover, the fluoride added to toothpaste and the tap water in many countries is arguably bad for you. However, if you'd still like a little abrasiveness without using chemical-laden toothpaste, try baking soda.
In fact, baking soda is an ingredient that is often added to most commercial toothpastes anyway. By using it alone you're simply avoiding also putting a lot of other chemicals into your mouth.
If you dislike the taste, try adding a little stevia or xylitol to the baking soda. This sweetens the mixture while keeping it all natural.
Don't forget to brush your tongue!