I switched to red seal natural toothpaste and havent had sensitive teeth since. Used to have really sensitive teeth so you could try that.
Im a bit divided on the flouride thing, as studies Ive read have conflicting results. Seems you find what you want to. Think id prefer to err on the side of caution and not have it in our water. However if you do do flouride, I read topical application rather than taking it is supposed to be more effective.