I hunt with a small (40-44lb) female English Setter. She has a fantastic desire to retrieve. As such I use her for duck hunting. I hunt the Coastal Zone and South Zone. We do a fair amount of work for diver ducks when the water is cold. I have never had a problem with her making a retrievein cold water. Like your dog, she sees the bird and is keyed up waiting for the go ahead.
I do, however, have a problem watching her shake and shiver after the retrive. I use a towel to dry her immediately following the retrieve. I then have 2 wool army blankets. One to lay on and one to be wrapped up in. She wears a fitted neoprene vest. I agree she is warm as toast and relatively drry under the vest in short order. She will let me completely cover her, head and all, with the blanket. When she has warmed back up, she pokes her head out.
I was thinking of trying a portable propane heater in the boat this season. Haven't decided just yet.
I was also looking at one of those pressure sensitive mats that heat up to about 105-110F. They can run on battery. I was thinking of setting up a deep cell battery in the boat that would warm the pad for a day of hunting and then just be recharged at night.
In the end though, I decided to put money down on a Chessie pup. Yeah, that was probably the most cost effective thing to do
Still plan to take the Setter though. I can't leave her at home!
Fear God, love your neighbor, and hunt ducks. . . . The Duck Commander