jehmco has good, quiet pumps, I don't know what the shipping would be like for the UK though...
you could probably get away with just using them to move the k3 and not have any disks in the tank, that's what I do. I figure the water is getting aerated from splashing into the sump and the stones powering my k3 chamber. pretty sure mine is the 15 liter per minute and it pushes the k3 just fine with 2 big airstones.