Hi, I know will probably get a lot of heat for this suggestion but I would look into getting a two piece spearfishing hooded wetsuit that is unlined on the inside or more widely known in the industry an open cell wetsuit. To further explain, the outer side is usually a strong jersey material for protection and the inner material is raw neoprene which sticks to your body like a second skin, moves with you, and doesn't allow any water to penetrate.
I purchased a 3mm and found it to be as warm as my bulky 7mm semi-dry scuba suit. As an added benefit, these spearfishing or freediving suits are much more thinner and flexible. The only downside is you have to use a mix of unscented hair conditioner and water to get into the suit itself but taking it off is very easy so it's a minor inconvenience. Plus, the hair conditioner mix conditions the suit and makes it smell and feel wonderful on your bare skin. I speak from personal experience as an AOW/Nitrox diver and wouldn't go back to a regular scuba suit. [emoji6]
Here's some pictures of them. I like the high pants vs the farmer john style but the latter will be warmer. Freedivers and spearfisherman are in the water usually much longer than scuba divers.
Anyway, hope this helps!
http://www.neptonicsystems.com/Rob-Allen-Dual-Camo-Wetsuit.jpg
http://cdn3.volusion.com/psrbn.xmcnq/v/vspfiles/photos/M2YRCW-1.jpg?1438327635
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