You need to understand that, unless ou plant a dwarf shrub, you will have to prune it each year to keep the size in check.  You also need to consider that anything planted there will be exposed on all sides to the weather so possible sunscald of an evergreen.  If you plant anything with leaves, they will drop in the fall so there will be bare limbs in the winter.  Best would probably be a viburnum, a native shrub, but only one that is small in mature size.  Some can get very large.  But it will lose its leaves.  Arborvitae will remain green but you must make sure to keep it watered until the ground freezes and possibly protected by a burlap fence.  Here's a link to steps: https://extension.umn.edu/planting-and-growing-guides/protecting-trees-and-shrubs-winter  When shopping at your locally owned garden center, read the label information on possible shrubs.  Also, ask the personnel there for their recommendations. Again, I remind you to look at the mature size of what you purchase.  The closer it is to the space you have available, the easier it will be to take care of.