It's pricey, but raw liquid cacao is the way to go if you want something without sugar that's easy to blend in coffee. Available as "Cholaca" on Amazon: https://www.amazon.com/gp/product/B013U5LVEK
I used to use cacao nibs, but this has a vastly superior flavor.
So I'm doing a peppermint chocolate porter for this holiday. I just brewed my house porter thats super yummy.
Recipe here. https://www.brewersfriend.com/homebrew/recipe/view/529857/santa-s-little-helper-2018-chocolate-peppermint-porter.
For chocolate I'm adding unsweetened choloca to taste when I keg. Kinda pricey but oh well.
https://www.amazon.com/Cholaca-Unsweetened-32-Ounces/dp/B013U5LVEK
Adding peppermint extract also at kegging to taste.
https://www.heb.com/product-detail/central-market-pure-peppermint-extract/977795
Cheers
Edit: I settled on peppermint extract after much research. Seems like its the most controllable and more consistent than making your own tincture. Just get a high quality one if you go that route.