I like the Chaval electrically heated gloves or mittens. They have a self-adjusting thermostat and an all-day battery. Friends like the Outdoor Research electric gloves or mittens, and they carry an extra pair of batteries for the afternoon. The Chavals have a nice extra--during the recharge period there is heat inside the gloves to dry them. Chaval's early season sale:
https://www.chavalusa.com/
As noted above, it's mainly about blood circulation. The brain needs to keep itself warm, so it draws warm blood to it at the expense of the extremities. Next in line are the vital internal organs in the body where the brain sends warm blood and cuts off flow to the extremities. Fingers and toes and hands and feet are expendable--we don't need all of them for survival. Try wearing more head insulation than you expect to need--an extra warm helmet liner or balaclava and your hood up over the helmet. Wear more body insulation than you think you'll need--an extra down vest or whatever works for you. See if this helps. Caffeine can have an effect on vascular flow, so try a morning without caffeine (no one said this would be easy) and try normal morning caffeine plus coffee or tea during rest breaks--see if it makes any difference for you.
Raynaud's disease is an extreme lack of blood flow to the extremities in the cold. If your hands are white when they're cold, consider it.
https://www.mayoclinic.org/diseases-conditions/raynauds-disease/symptoms-causes/syc-20363571 More heat added to the affected areas with heat packs or electric source as well as more head & body insulation probably is the best route. For the cold thumb, try mittens big enough to wear warm wool or poly gloves (not thin liners) inside.