Yo Kelpdiver-
Here's a fun trick. Buy a couple of rechargeable warmers that you can slip into your suit just before you jump in the water. You'll find them on the internet under "reusable hand warmers". If your suit back-zips, get the biggest you can find, because you won't be able to put in or replace it once your suit is zipped. I have used these things for years, and I love them. They are food grade sodium acetate ( clear liquid) in a plastic pouch, from pocket handwarmer size to bigger. There's a little goodie inside, looks like a dime. When you pinch it, a little grain of some catalyst comes out, the liquid goes white and milky, and heats up to about 120 degrees...and stays hot for about half an hour. I've talked to a chemist professor friend, and he says it is basically a saturated salt reaction. How you reverse the reaction (when it is done and cold), is throw the pouch in boiling water for 20 minutes, and it "reloads" (reverses and makes ready) the next reaction.
When I had a less than great wetsuit, I used to have my buddy put one of these things (a big one) around my small of back and zip me in. Jeez, I had to gear up and slam in to that water fast! It was like being in a hot bath, and so then was the water for most of the dive. That suit was classic farmer john and front zip jacket. So when I began to get cold toward the end of the dive, then hell I was cold anyway, so I zipped down my jacket, and put a pocket sized warmer into each armpit and zipped back up. Worked Great!
Now I dive an aqualung superstretch 7 mm back zip, with their hooded sleeveless vest underneath. It is a *really* comfortable suit, but once I'm below about 40 feet here on the CA Northcoast, I do feel the cold pressing in, especially from pelvis down. I can actually shiver, but with activity or closer to the surface, I warm right back up in it. I live with it. However, if someone could invent a thin little vest or unit that you could have under a wetsuit, say, battery powered in a sealed unit...Wow! Til then, I am considering just cramming one of my heaters from the hood's chin, down my neck, and having that wonderful little hot lump on my chest. I'll have to try this one. My buddy Eli got really cold one day, and I did that to him, but we were surface swimming to our dive spot. The water is 48 here. He got a fair amount of it down his neck with that warmer as I stuffed it in. He just about ran back to shore. But from a kayak, this would be cake. Or laying back, on the surface, you could pull out your chin and have your buddy just slip it down your neck without flooding you out. Hell the moment's cold would be even worth it. That is assuming you back-zip. If front, hey, just go for the armpit routine; keep 2 more in a pocket for later.
Good luck!
Peter