Right, I'm going to call this the last post in this particular journal as I'm running out of things to update about. I can't thank everyone enough for their support and general advice and awesomeness.
Kaze is doing very well but his age is beginning to show, his eyes are gradually clouding and he's resting more and more, he has also scratched his back again and I don't know what on. I'm absolutely 100% certain that the aquarium is safe for a betta, the driftwood has no sharp pointy bits and the plants are all fine so I can only assume that it is Kaze himself doing the damage somehow, maybe he's just not seeing things well... I don't know.
I have considered moving Kaze to a smaller aquarium with no driftwood but I really don't want to do that. I'll give it more time, maintain water quality and keep a very close eye on him. If he gets any worse I'll have to see about something more suitable (or just rip the driftwood out and put something else in there).
The driftwood still floats. If I end up unable to continue using it in the fish tank I'll yank it out, see if I can bake it then sit it in my room as a necklace rack or something... not quite the right purpose for such a lovely piece of wood but if Kaze's hurting himself on it and it won't sink then there's no point keeping it in the tank.
I do believe that it is entirely possible for the wood to sink in time but seeing Kaze hurting himself more and more I'm beginning to get very concerned.
Regardless of his back scratches and other problems he's still a very happy and interactive fish. He continues to jump for his food and when he isn't resting he is exploring and being a general goof. Right now he's trying to settle on a leaf of anubias that is half emerged... d'oh.
Love this animal.