Everyone reacts differently, but I think you could just stop cold. You aren't post-menopause so you've got some hormones doing their thing. I think of it like people don't taper off birth control pills, so stopping hrt shouldn't be any worse. If you're nervous about it, you could cut your estrogen in half for a couple weeks and see if you notice any difference, then decide if you need time to adjust to that lower dose, cut your dose even lower, or just quit.