Those space dimensions make for a short list of plants. Here are some possibilities and comments.
Nandina - standard types reach to about 6 feet tall. However they can spread slowly so you will need to dig sucker plants on occasion.
Dwarf Burford Holly - Slow grower to 4 to 6 feet tall and wide. Can be kept to about 4 feet wide with prunining.
Wichita Blue Juniper - Moderate grower to 10 to 15 feet tall, 4 to 6 feet wide. Larger with age so you would probably need to remove it down the line.
Weeping Yaupon - These have an upright trunk and then arching/weeping branches.
One of the many topiary types of juniper sold by Monrovia. These are some work to maintain the nice shape and form, but are very attractive.
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