On paper at least, the mature height and width of 'Emerald Green' and 'American Pillar' Arborvitae varieties overlaps nearly completely. (References to size may vary from source to source as it will partly depend on growth rate that can vary in different climates, plus growers referring to different ages of plants in measuring size.) 'American Pillar' sounds like it's a faster grower according the the breeder, but we don't have personal experience with this cultivar due to its newness. Both of these are varieties of Eastern Arborvitae (Thuja occidentalis), a conifer known to be very palatable to browsing deer. Even though they might not frequent the yard, a plant this desirable to them is risky to use, since foliage they remove by browsing will not regrow, so the plants may end up with the bottom five or six feet of growth greatly reduced or removed.

Monocultures (planting the same plant in a sizeable row/group) also risk pest outbreaks that make control more difficult and costly. For Arborvitae, the pest of concern would mainly be bagworms, which can be difficult to spot when they're young and easier to manage. This is one reason a mixture of species is recommended, though we understand your desire to keep this screen as space-conserving as possible.

The tall evergreen in the photos appears to be a blue Colorado Spruce, though it's hard to tell without closeups. (Or perhaps the one you mention is different tree.) In either case, from a 60-foot high tree, spacing will depend a bit on what's being installed and how shade-tolerant it is. Since most evergreens prefer sun, however far away its shadow is minimal is what would be best. In terms of root competition (especially if you're using a shade-tolerant plant closer to this tree), then you may have to experimentally probe the area with a shovel to see how far out the roots remain in the way. As an educated guess, this might be a minimum of 15 feet.

Since deer pressures are not likely to lessen substantially any time soon, and if no deer fencing is used, then we recommend you focus on species known to be unpalatable to them. Nothing is deer proof, but since so many of the candidate plants would suffer notable damage from exploratory browsing, it's safer to assume it's a risk. A sample list below of plants to consider is for sites in full sun (6+ hours of direct light) unless otherwise noted. Not all will be very narrow, but few such options exist. 'Emerald Green' Arborvitae would mature around 20 feet tall and about 5 feet wide (which is pretty slender for that size of plant), and some of the below are similar in stature while others are larger.

• Eastern Redcedar (Juniperus virginiana), which is locally native and benefits birds, includes several cultivars with blue-gray foliage and/or slender growth (though possibly too skinny); other Junipers, like Rocky Mountain (J. scopulorum) and Chinese (J. chinensis) could work and expand the range of variety options
• Western Arborvitae (Thuja plicata), like variety 'Green Giant' or 'Forever Goldy', 'Golden Spire', 'Steeplechase' or smaller growers 'Sugar and Spice' and 'Tiny Tower'; this species of Arborvitae overall is not nearly as tasty to deer as the Eastern
• Japanese Cedar (Cryptomeria japonica)
• Arizona Cypress (Cupressus glabra)
• hollies (Ilex) with very prickly foliage, such as 'Dragon Lady'; hollies have good tolerance for shade
• False Holly (Osmanthus heterophyllus) variety 'Fastigiata' and possibly 'Gulftide'; not going to get too tall compared to the rest of this list, but might be a useful filler between higher growers; good tolerance for shade; very fragrant tiny blooms in autumn when they're old enough

Miri