Yeah, thats a tough one. You dont want to roast when youre in the boat. But you do need serious insulation when youre in the drink. Plus you arent quite thermally equipped for cold North Pacific waters.
The Merino 1 Crew
I suggest wool. It keeps you warm when it gets wet from sweat or water, and it has a wide thermal profile so you wont always cook when you are dry. Plus its a lot more comfortable than wearing thermal shirts and a wetsuit under your dry suit.
Probably two layers. Start with a light layer, such as Patagonias Mens Merino 1 Crew ($89). I like this because it combines wonderful Merino wool with some polyester, which is great because polyester wicks well and dries fast. Its a great companion to wool.
Over that, a midweight layer. Good candidates are Icebreakers Boldyfit 260 Long Sleeve Crewe ($90). A great pieceI wear it under a light shell as a winter mountain-biking base layer. Very warm but not that heavy. Heck, get TWO of them and layer them one atop the other. Beats other alternatives.
SmartWool makes something very similar. That companys Midweight Crew is $75, made from wool thats really the same as Icebreakers, and works great as a warm mid-layer.
The third option is to overlay all this with fleece. Marmots Reactor Fleece Jacket ($80) would add a bit of loft to a wool base, is very light and form-fitting, and is really warm for its weight. It would work atop either the light Patagonia, the heavier Icebreaker or SmartWool, or both.
All of these pieces have below-waist analogs. Probably a single midweight layer would work there.
I recall once jumping off the back of a boat in a snowstorm in February in the San Juan Islands. I had on a wet suit. It was 33 degrees. Water felt warm. So buck up, lad.