Further to my reply on "the darkside", the pockets that I got from Divers Wearhouse are not flat, they have folded sides, which, I guess, opens about 1 and a half to two inches at the sides. (Meaning that you can get much bigger stuff in the middle!)
My one comment would be to attach a "D" ring inside to clip stuff to!
FifthD in the USA make/sell excellent bellows pockets and they are only $30 (dollars) each. I have just got a pair for my suit. They have three drain eyelets in the bottom and two s/steel eyelets for attaching shock cord loops(to avoid d-rings). The pockets fold flat when empty.