Dying cat: urgent please help?

my 17 year old cat is dying right now. He was at the vet last week and told he had a myriad of problems, bradycardia, cancer, pleural effusion etc. He was still acting somewhat normal so we delayed euthanasia until he was showing obvious signs of pain. Right now he is lying on the bathroom floor, slowly dying and we are unable to move him. Does anybody have any real advice on what to do? He groans every so often but otherwise his respiratory rate is slowly decreasing hour by hour and its clear the end is within a few hours. Anyone WITH EXPERIENCE in the matter have any advice on how to make him comfortable?