Most of the English holly (Ilex aquifolium) cultivars will grow into trees, as will I.x altaclerensis, I. latifolia and I. perneyi - I.x attenuata makes a small tree, 12-30'. These are European or Chinese species or hybrids, for the most part, with some admixture of American ones. Most of the other species, and the many hybrids, will be shrubs or small trees.

There are so many varied Holly cultivars, and I am not sure what is available, or suitable, in your area. Your best bet may be to look in regional gardening books, and to ask at several good, and large, garden centers in your area, to see what is available locally - while availability isn't always an indication of what is truly suitable, it can tell you what is out there.

Blue Princess can grow to 12 - 15' tall in the right conditions. perhaps taller. It is Ilex meserveae if you want to look it up.

Mine is about 6' tall and it has grown about 2' in 3 years in morning sun in tough soil conditions. (competing with pines and oaks nearby)

What is your zone?? If your winters are not too severe (zone 6 and higher) Nellie Stevens is known for both its rate of growth and size.

The OP is in the UK somewhere, which is why i was so general - I don't know how the meserveae hybrids do in the UK, but they really aren't trees - well, I guess you could say that 15' is a SMALL tree.

How large do the root systems grow? Is it safe to plant the Blue Prince/Princess variety in a bed bordering the house?