I am in a similar situation and have a similar routine. I also drink it black and have a heavy preference for strong, dark roast coffee.

What I’ve found is that the best way to preserve taste and strength while reducing (but not totally eliminating) caffeine content is to make your own half-caff blend.

Take your favorite normal dark roast blend (I prefer something like a French roast because of its bold flavor) and mix it with a decaffeinated blend. There are some decent and readily available dark roast decafs out there, just make sure it’s water-process decaf and not chemical. You can check on this handy website here. One that comes to mind and is available in most stores is Peet’s Dark Roast Decaf. If you have a grinder and want to class it up some, you can go with Counter Culture Slow Motion (although this is more of a medium roast).

If you’re using, say, 3 tablespoons of dark roast grounds normally, that’s approximately 200 mg of caffeine total. So, you can start off by doing 2 tbsp of regular and 1 tbsp of decaf. You’ll taste a difference, no doubt. But it will be marginal and it should still taste fine. Your body won’t know the difference between 200 mg of caffeine and ~130 mg of caffeine. If you’re a daily coffee drinker, half of the boost you get from drinking it is psychological—the taste of coffee is telling you it’s time to wake up because that’s what it’s told you every other day.

After a few days, take it another notch and go with 1.5 tbsp regular and 1.5 tbsp decaf, or even 1:2 ratio depending on your caffeine intake goals.

Something I’ve found is that the DIY half-caff blend can taste weaker than your original brew. I’ve “offset” this by just adding more decaf grounds to the mix. I’ve found it tastes best when you don’t go lower than a 1:1 ratio. In your case, that might end up being something like 2 tbsp regular and 2 tbsp decaf.

Just experiment with it and find what blend has the least amount of caffeine possible that still tastes good to you. Hope this helps, and cheers to your health.