i'd post this in the regular forum and you'll get lots more advice!

I have a yew of some sort that was given a secret santa gift 12+ years ago (the person thought it was a rosemary, so i don't know the variety, but it's a yew; it set berries recently and sealed the diagnosis). At any rate, it has just grown mostly straight up, at a slow but steady rate. It's now about 10', and only about 3' wide, on average. I say average because it has 2 dominant stems which have flared slightly as it's grown. I think it you kept them to one, they'd be like many of the other slim jims of the plant world.

That's easy..skypencil holly (non-prickly). A pair of them should do nicely for the diameter you desire and they will reach the full 10' because that's their max height.
I've been tempted to use them as living trellis for a nice clematis.

There were a pair of enormour columnar Peach trees at the Arboretum, removed when the new visitor ctr was added. I happened to spot some little ones in one of Plant Delights propogation greenhouses. Don't know what became of them. I think Crimson Rocket may be a dwarf.