I played the mixed trinity setup early in the expansion, but quickly gave it up and went with all same class teams.

Back when I was running trinity I kept everything in IsBoxer, created a menu and placed it next to the party frame. I just click the button next to the name when heals were needed. One button to heal, one to cleanse, I think I had 5 buttons for each toon but cant remember what I had the rest do. For the most part I depended on the disc priests dps rotation to heal everyone. And like you I couldn't keep up during the tough times.

I just gave up trying to make it work, would rather go the fun route. Every expansion seems to change things, maybe the trinity team setup will make a comeback in BfA.