I'm using kit made by Condor (available from Military1st) and it has tonnes of room and adaptability. Quality is pretty good as is the price.
I was bigger (18 and a half stone) when I started and since losing two stone in weight I've not had to change my chest rig/hydration pack combo.
I'd happily recommend Condor as an alternative to Warrior, although I know how good the Warrior kit is.