another view

bushes you cant see, behind maple along other wall

What part of the country? What zone?

It's difficult to provide relevant suggestions unless when know stuff like that.

Jim

oh sorry, norhteast, zone 6B

Yews and box woods can both be trimmed and are evergreen. Both tolerate part sun. Both may need some water from time to time, your existing yews look a little thirsty maybe? I could be wrong but doubt any evergreen is going to stay green to the ground tucked right in behind that lovely Japanese maple. And don't forget to trim them so that the top is slightly narrower than the bottom to promote light penetration and therefore fuller foliage below. In front you could put an evergreen Rhododendron but they don't like deep shade.

i think it would look better if you simplify the overall scheme. You could eliminate the competitive, overlapping vertical shapes and arrange the layout to something bolder, but simpler. Can't tell what it is, but the shrub (if it is) at the right front looks like it might make, a nice, low-maintenance backdrop. If it is not suited, then look for something else that can be 3' x 3'.

I'd suggest removing the plants behind the maple and the conifer near the stoop. The maple is lovely now and will be very distinctive there in a short time. Find a low growing groundcover for the areas where you take out the shrubs.

HTH