The purpleheart armoury has octagonal staves (staffs?) of hickory and ash. http://www.woodenswords.com/WMA/index.htm.
I train with a octagonal "escrima" stick that I made myself. Though I think in your case, a simple rattan stick will do. (They don't come octagonal). Though, if you're planning on doing only solo work, I would go with a heavier stick. You don't have to be an expert to go heavy. Working with heavier sticks promotes better form, better twirling and better workouts. For sparring/partner drills, stick with rattan.
For anyone that hasn't used octagonal, I recommend at least trying it out. It provides a better grip, which makes sense as the hand and fingers is segmented. But don't try it with sparring!)
Besides that, I would also recommend a proportion of around your armlength. The proportion I like is slightly shorter so that when you twirl it horizontally with your arm extended, it will not hit you in the head.