I dive those temps a lot. If diving wet I normally do it it with a 5mm Reactive (equivalent to a 7mm) full suit, 7mm hood, 5mm boots and 5mm gloves (all Reactive as well). Did a series of Rescue Course dives as the 'victim' and lasted through 25 minutes of lying still at depth. I would normally prefer a drysuit but mine has had issues for a while and has been back in for repairs two summers in a row.
I think you might be fine with the 3mm shorty over a 3mm full but I would add a thicker hood, boots and gloves... unless you are impervious to cold (I know an instructor who teaches in those temps with no sleeves, hood or gloves)
I think you might be fine with the 3mm shorty over a 3mm full but I would add a thicker hood, boots and gloves... unless you are impervious to cold (I know an instructor who teaches in those temps with no sleeves, hood or gloves)