I've got a couple Bougies myself and they are nice because they give you a ton of growth and you can do a lot in a short amount of time (relative to other species).
I think the key with the wiring on these is getting it on super early. They are very brittle and don't take well to the kinds of bends that you can get in a juniper or pine for instance. So when new growth emerges you have to act pretty quick to get it headed in the right direction before it gets too thick. On all of my plants the new growth tends to come out of the trunk or main branch at sort of a 45 degree angle so you have to act quick if you want it to be closer to perpendicular.
FWIW I've found with the Bougs I have planted in the ground (landscape only, not bonsai) that if you really want them to thicken you have to let the whole thing kind of go crazy. So I might suggest letting them basically run wild until you get the trunk you're looking for then cutting back hard and starting to work on branch placement. You might already know this but you can cut these things back to a stump that is flush with the ground and they'll still throw out 10 new shoots all over.
I believe
@Carol 83 has some bougies out in your zone, she may have some additional feedback for you!