Besides evergreens, winter interest can be had in grasses that dry and persist, and twigs. I would shoot for tall grass in the corner. Many Miscanthus might get too large, but a cluster of several Calamagrostis might work out to create a dried arrangement in the winter time. I've seen many examples of 'Karl Foerster' around the Chicago area.

My 2 cents is that I would go for a single boxwood dome shape below the window as opposed to a skinny hedge of them.

My growing situation is really different from yours, since I live on a large piece of property in an area that has more acid and well-drained soil, but I have the same issue with winter interest. I try for a range of items to create winter interest:

evergreen groundcovers (here's a thread from the New England forum that has a bunch listed that you could research for suitability to your area or ask on the Great Lakes or Midwestern forums)

evergreen woodies (look at broad-leafed plants like the boxwood mentioned above as well as small, narrow or low-growing conifers)

colored or interestingly shaped branches or attractive buds - One thought here is a really small red-twigged dogwood, Cornus 'Kelseyi' which should stay under 3 feet in all directions. Cutting the branches back periodically in spring will keep the twigs' color bright. In larger gardens Japanese maples or magnolias are really nice in winter, but you don't appear to have the space here and since space isn't a challenge for me, I don't have much to suggest as far as specific small plants.

Berries (such as hollies, hawthorn, or crabapples though all are most likely too large for you.) No sure what small berry-producing plants there are. Perhaps you could ask for ideas on the shrubs forum for plants with winter interest for a very small garden. Maybe a climbing rose with attractive hips would work.

Dried foliage or seedpods (such as the grasses)

Non-plant items such as trellises, winter lights, weatherproof art, and food or water to attract birds. Right now you have a large wall space that could be utilized to add interest: an artistic trellis with the clematis pruned back and strung with white lights (instead of the basic one currently there with the remains of the clematis - you want to prune back type 3 clematises like yours between hard freeze and spring growth to a couple buds per stem, so doing it now will give you a nicer view) and/or a flat wall sculpture mounted in the space above the door. Adding a heated birdbath will bring birds to the garden to add movement and color. Even a large pot on the patio filled with winter branches and lights adds to winter interest. Check out some of Deborah Silver's winter 'plantings'. I like having garden lights that aren't necessarily just holiday lights but that add to winter interest when it's getting dark as early as 4:30 in the afternoon. I particularly like this arrangement of curly willow and lights, which makes me think of the warmth of a blazing fire.

As you plan, think about the way adding snow or ice will change your views. You want things that will emerge from the snow and are enhanced by the snow such as branches, whether evergreen or deciduous or non-growing, as well as plants that will add interest from structure, color, or movement to the garden when there isn't snow.

Just wanted to add that if you look at Yaardvark's two sketches (the one that you posted from another thread and the one he posted on this thread) note the layers. They have a groundcover (evergreen is good for winter interest), something on the garage wall, and shrubs. There isn't bare ground or holes. I'd most likely add pots with annuals rather than plant them in the ground, as annuals will leave you with bare ground in winter.