To the OP, if you have not yet found gloves or mittens that will keep your hands warm, I doubt you will find any that will do so and be acceptable for hunting. My hands typically don't get cold if I'm walking, but they do when I sit all day. In those situations, no mitten or glove has worked for me. I guarantee you will never have cold hands again if you do the following.
First buy an insulated hand muff that straps around your waist. Something like this:
https://www.sportsmansguide.com/pro...PLA&utm_source=Bing&utm_campaign=CI&gclsrc=ds
I am not endorsing that particular hand muff, its just the first one that I could easily find on an internet search. Many companies make them.
Then you buy either the chemical handwarmer packs, or if you really need more warmth, you buy a Zippo hand warmer, like this:
https://www.zippo.com/collections/hand-warmers/products/12hour-realtree-hand-warmer
Your hands will never be cold again and it won't matter what gloves you choose to use. I use thin gloves that are easy to take on/off. In fact, you will have to be careful to not let your hands get so warm that they sweat if you use the Zippo. When I use the Zippo, I typically have the heater going in the hand muff and put my gloves in there with it. Then I keep my hands inside the muff as well. Hands are perfectly toasty. Then I just slip on the gloves if I want to take my hands out of the muff. Sometimes I keep the gloves on and put my hands in the muff as necessary.
The other advantage to this approach is you can adjust easily. Only a little cold - just put your hands in the muff as necessary. Colder - put a chemical handwarmer in the muff and put your hands in as necessary. Very cold - use the Zippo in the hand muff and put your hands in as necessary. Extremely cold - use the Zippo and keep your hands in there until you need to take a shot. Any colder than that - stay home.