What herbs work well in coffee, and is a crystal okay to add?

For a gentle start, try a pinch of culinary cinnamon or cardamom mixed into the grounds. They can take over quickly, so keep the amount small at first. Dried culinary lavender or mint might work too, though both can change the flavor a lot.

Use herbs sold or gathered for food, not plants chosen only for their spiritual associations. If you forage, be certain of the identification and that the spot is free of contamination.

The ritual can be in the intention as much as the ingredient. You could pause while measuring the coffee, choose one food-safe herb that fits the mood you want, and take a moment with the finished cup. No need to make the recipe complicated.

I would keep crystals out of the drink. Put one beside the cup or on the counter instead. Stones can have coatings or residues, and you may not know what could leach into hot liquid.

One practical note: adding a lot of plant material to the filter can slow the drip or leave grit behind. Start with a tiny amount, and consider steeping a small pinch in the brewed coffee instead if you want to test the taste without changing how the grounds filter.

Skip unfamiliar medicinal herbs, especially if you have allergies, take medication, or are pregnant. A food-safe flavoring amount is a different thing from using an herb as a remedy.