A stunning evergreen shrub to place at the back of your garden bed is the Castle Wall™ Blue Holly. Growing to an impressive 5 to tall, but only 3 to this holly is perfect for mid-sized gardens as it’s narrow, pyramidal shape won’t overwhelm - Picmia
Keep the garden vertical. That's why it's good to look for shrubs and trees that max out interest as they grow up, not out. Try dwarf varieties for a small backyard, as well as more columnar evergreens (bonus—they boost wintertime interest, too).