Not all customs are created equal. After buying a "motorcycle specific" pair I wasn't terribly happy with. I called Westone and talked to a guy named Rich Anesko, who was super helpful. Loads of useful information about what to order, what materials to use, etc. I would go with Westone again, but probably a call to any reputable maker might be worthwhile.
A few things to ponder...
Customs won't actually isolate more than properly fitted disposable foamies will. Most of the experts will tell you that right up front. They can get real close, but the 33NRR foamies will still block the most. The thing I like about customs is that they're always there, and super easy/quick to pop in.
Helmet shape and fit can make otherwise well-fitting customs not work so well. If (and how) the helmet liner deforms the shape of your outer ear, it can easily break the ear canal to plug seal. In other words, customs might require you to get a different helmet. And it's kinda impossible to test before they're made.