NightWing wears taller black boots, you can see them pretty good here in this figure based off the Hush design.
I would recommend Eastern Coast costumes, http://www.911buycostume.com/Pages/gogoboots/boot01.htm
I got the boots for my Robin from them, and my brother got his Batman boots from them. Go to that link and go about half of the way down the page, and look for their “Military Riding Cavalry Renaissance Jedi
Boots Black” item number 1404BK. Less than $40 for a pair of good boots, I’m very happy with mine, quick delivery and good quality. They do have a zipper up the inside, but it’s not that noticeable if you ask me.