You mentioned you had an old fashioned Nandina domestica. One option is to contrast the upright form of Nandina domestic by pairing it with a mounding barberry. First Editions Cabernet Barberry has rich burgundy and purple foliage that holds up through the heat of summer and stays small. Or, if you're looking for a plant with warmer accents, Citrus Tart Potentilla is another wonderful plant for colder parts of the country and into southern regions, too. Potentilla has golden flowers in the summer and would look lovely when combined with barberry, Nandina and Happy Returns Daylily. All are hardy plants that are incredibly easy to grow.
If you have room for another plant or two, consider planting Eternal Sunshine Abelia, another mounding plant that grows great in warmer climates. The new growth is copper-orange and will look nice combined with colorful barberry foliage. Flowering early, Eternal Sunshine will be covered with light-pink flowers that attract butterflies and hummingbirds. Another plant that thrives in warm climates is Crimson Fire Fringe Flower, a compact red-leaf Loropetalum. You are in the right zone for this plant! It will be colorful year-round, stays compact and flowers mid-spring.
I know it can sometimes be hard to visualize mature plants and create a garden based on plant descriptions, which is why we recommend browsing our Yard Design Ideas to help get you started. Please let me know what plant or plants you select. I would love to see a photo or two of your garden.