I've added an inch and a half above the waist, so hopefully that will be enough to make the waistline fall in the correct place.
One thing I have noticed is that the upper welt pocket tends to fall open, it seems as if the weight of the coat pulls it down. If this isn't resolved by having a proper sized body inside the coat I guess I could stitch it shut, but I'd be interested to know what the proper solution would be.