In an attempt to not freeze so quickly with winter sailing I have added to my wetsuit and flotation vest a chemical wetsuit heater, a polypropylene rashie, and most recently a spray jacket.
The spray jacket has been the best heat saver of them all. I wear it under my flotation vest and harness, so it filling up with water is not a problem. It helps a lot to prevent chilling when standing around in between sailing, but I was surprised how much it helps to keep the cold out when in the water water-starting.
So if you feel the cold and don't have a spray jacket, it's well worth the (relatively small) investment.
My winter sailing time before chill enforced retirement has increased from 30 minutes to 2 hours.
I found if you are in the water a lot warmth from the wetsuit heater quickly abates, but it is wonderful to put on after a sail to warm out those chills.

My feet are now the limiting factor. Recommendations for warm footwear that isn't too hard to slide out of foostraps please...