The souls I'm meant to chuck at him spawn way too slowly, and inconsistently to boot (some times the first will spawn the second the 'boss fight' music starts, sometimes I have to wait for the first one for as long as I have to wait for the second, which isn't the same length of time every time, but always too long). Is there a trick to getting them to appear?

Further issues: The hand that's meant to spawn and form a platform sometimes appears way too early or way too late, so that by the time I have someplace to jump, the bone dragon is already moved on to attack again. Sometimes I can't even jump on the platform when it spawns (landing jumps and wall clings seem to be a glitchy thing throughout the game).

It sounds like you have clipping issues. I don't have that problem at all. It's one of those frustrating games that you just need to practice in order to beat, like Conkers Bad Fur Day.