Thanks guys. Because of my shape keeping a belt in place wont be an issue; think of a dumbbell in both senses. Main issue will be the top and bottom of weights digging into my ribs and hips.
So on your advice I went into a dive shop and got the smallest pocket belt they had and 4.2kg of weights. Might pay to do a 1/3 2/3 split on one to give me options.