Before you embark on this project, you should be aware that a pretty serious issue exists with various species of boxwood that may make this a very frustrating experience. A very severe and non-treatable fungal disease - boxwood blight - has been sweeping through parts of the country, focusing on New England but now spreading, and killing off boxwood plantings. Dwarf English box, Buxus sempervirens 'Suffruticosa', is extremely susceptible.

Boxwood Blight

I might want to consider what other plants you could use for a similar look that would be less likely to generate problems down the road. Japanese holly perhaps?

Are there dwarf versions of the Japanese holly? Thanks for the reminder about the blight, I forgot about it.

Ilex crenata 'Helleri' would probably be my first choice.

Another option might be one of the small-stature, small-leaf rhododendrons.