I would suggest the Aqualung Mikron as have several others. It is sure a tiny little thing.
However, it is also worth considering the hose that might tend to pull the regulator to your right. You can put a swivel at the mouthpiece and eliminate some of the effect. You can also use a Miflex hose (with or without the swivel) to get a little more flexibility. I do note, however, that the manufacturers are catching on. The Delta 4 (Oceanic) hose is quite flexible right from the factory and the Delta 4 comes with a swivel (in one variant).
But, since mouthpieces tend to be interchangeable, there is a limit to how small they can get. At the reg end of the mouthpiece, they are all the same size. There may be an exception here and there.
Richard