I have an 11" wodent wheel that is good & not too huge. I think the Carolina Storm wheel is supposed to be good too but I don't know about sizing as we don't get that here.
I know what you mean though, I struggled to find a wheel as a lot of the 12" wheels once they're on stands are pretty chunky but I've been pleased with my wodent wheel. Better to have a good size wheel & take something else out, I think than a too small wheel. He needs a straight back when running, not back arched & nose in the air