I have a friend who cosplayed Professor Layton once, and he has a tall hat himself, if that's the main thing in question here.
To give the hat its structure, she used a material that was essentially a grid of flexible plastic; I'm not sure what it's called, but she got it at a Joanne's, the results were fantastic, and it was inexpensive as well. That may not help much, but if that seems like something that could help you, I could always get in contact with the friend and ask her what exactly it was. XD But basically she rolled it into a tube (and possibly trimmed as necessary) and then wrapped the outer materials around it. I don't know all the details, but it ended up looking fantastic and really authentic, so perhaps something like that could work well for you?