At risk of a thread-jack (we can move this discussion to your training log, or mine, if preferred), I'll see your one-armed swing and raise you the one-armed clean and press. Something very primal about it, like lifting (somewhat) heavy stones over and over, and I think the combination of pulling, then pressing, is a bit more of a "complete" lift than the swing.
But we are getting sidetracked. Given that OP is a climber, I think the advice for a one-arm lift vs. two-arm is sound. OP's going to have to decide on the right weight, but I agree that 12 kg is far too light, even though he's a small chap. I encourage the idea of a 16 and a 24, but if the budget does not allow, I second furo's advice to get a 20 or 24, start with two-armed swings, and build up to one-armed stuff.