Ulmus x hollandica Never have worked with it, but after some google searching it seems to be slow grower but a good bonsai species, has dense growth, Brent at evergreengardenworks sells them - perhaps he would be able to give you some good advice.
They break like glass, especially in winter. Small branches die without warning. This is not a very stable variety. Just one in a collection is enough.
Had a (could have been a nice) air layer fail on me last year, and this year only the bottom 1/2 decided to return to life, that excludes the layered area.
I have 2, one from cutting that was rooted easily around mid summer as a bare piece of kindling. They thicken quickly but have a very haringbone branching pattern.