I think it’s beautiful when plants are tucked in around rocks of different sizes. You can add something unique by using colorful plants.
Here's an idea: Start by placing larger rocks, pack in the soil and then add the plants and smaller rocks. Psychedelic Sky Buddleia has fragrant flowers that butterflies love and would be a good choice if you have room for a plant that matures 4-5’. If you want something a little smaller, try Blue Puffball Vitex. Either one (or both!) would look great in a garden with agave and ice plants.
You’ve inspired me to try something new!