You pretty much got it all right.
I've sat many bucks, and actually am the guinea pig that my friends use when resolving bucking issues, because for some reason I'm able to stick like glue to a saddle.
Usually whenever I feel a horse about to explode, or buck, I sit super deep in the saddle, shove my heels down as far as I can, and just sit back and wait.
You've just got to be prepared for either the buck or rear, and make adjustments for both. Plenty of times I've had horses rear first, then take off on a bucking tangent. You've just gotta pretty much go with the flow and remember to keep your balance with the horse, because thats normally how people get thrown. When the horse goes up, you lean forward. When they go down (head down & bucking) you lean back.
As long as you keep him from getting his head down, he shouldn't be able to process too big of a buck, which will be easier to hang onto. Normally when they rear first then go right into bucks is when you can expect a big explosion because they're able to throw their heads down then.
And I like what another person said on here... about turning him in a tight circle. If you feel him start to clam up, or start to tense up to buck, turn him in a tight circle. Once he learns that you've got his number, it should fix the problem.