Hi Rosanna, When working with women who cannot take estrogen for one reason or another, I have had very good results using bioidentical progesterone, 50-150mg daily.  I don't have extensive experience with estriol but really only use it for vaginal issues where it seems to be the most effective estrogen.  It has long been said that it has no impact on breast tissue.  This has come into question in recent years.  However, it is a very weak estrogen so would have minimal effect and I'm not confidant it would help so much with hot flashes.  You might also try flaxseed, Vitamin E 400 IU twice daily, and regular exercise which has been shown to reduce hot flashes in number and intensity. Good luck to you! Sandy