I had a heated vest (from a company called Eclipse IIRC) when I was riding year round. It was great under winter motorcycle gear or a snowmobile suit. The vest was plenty to keep my whole body warm. The only downsides on a boat are unplugging and plugging when you have to leave the cockpit and the power drain.
I sailed the Skagerak in April and crossed the Atlantic in May/June wearing Gill Atlantic foulies -- they have an inner jumpsuit in addition to bibs and jacket. I've been very pleased with the system.
For the innermost layer I'm a huge fan of Damart products. I was first pointed to them by a Chicago motorcycle police officer who said all his buddies wore them riding straight through Chicago winters. I carried #3 (medium) and #5 (super warm) level stuff sailing the Skagerak and then on the crossing. I never needed the #5 but I felt better knowing I had it. Damart has a very light presence in the US these days -- the last time I ordered anything it actually shipped from the UK. It is absolutely worth the hassle. No question.
Since I got back to the US and in the much more benign winters of the Chesapeake I discovered that Zippo (the lighter people) still make old fashioned fuel-powered hand warmers. I got one at a outdoor store and I'm sold. The next time I get the chance I'm getting more. On a full load of lighter fluid (3 oz?) it runs for 24 hours with a pleasant warmth. There is no open flame; it uses some kind of glassy catalyst material. Outstanding!
I also carry a box of the chemical handwarmers for guests who underestimate how cold their hands may get.