Since the spot is bookended by evergreen shrubs that bloom in winter maybe plant some non-woody plants that come out at the same time. Or something that blooms in summer, so as to extend the season. If you want it all evergreen and this is a sheltered sunny wall maybe choose one or more kinds of Hebe for summer flowers. Independent outlets here have large selections of these at this time. Apart from hardiness issues with the less frost tolerant kinds (that are nevertheless regularly offered here) all need quite good drainage. Be sure to find out the specific cold tolerances of any that may catch your interest.

would be a good spot for a little grass massing as well...

Here is a link that might be useful: nice in sun or shade, tolerates dry.

how about adding needle foliage to contrast with your broadleaf.... like a dwarf pine, Abies, or Tsuga? --best cultivars to be suggested by the experts on this site.