I need a plant which is evergreen and which naturally only grows to
approximately 3 feet.

Since nandina grows so well for you, you might want to try one of the dwarf
nandina cultivars, such as "Harbor Dwarf." I have 3. I planted them 4 years
ago, as knee-high container plants with about a dozen stems. They are still
only knee-high, but they have grown more stems.

Wendy
Wilmington, DE (Zone 7)