Ouch, sounds most unpleasant. Not sure my suggestions will be much help but first thoughts...
Assuming your bow hand is in the 45 degree rotation could you lower the knuckle angle and potentially get the bow weight further across the palm. Just thinking that a tiny shift in pressure *could* make a big difference. Just looking at the variation across top archers shows that a wide range can be effective.
I can see why you might not want to use a glove but have you tried tennis overgrip to give you a little padding? Anything from Tourna classic through to something thicker like a Pros Pro thick or Head Hydrosorb Comfort. Maybe even a gel grip if you are adventurous.
Most of the Koreans tape their grips, most use quite thin grips like Yonex Super Grap (honest that is how you spell it) but you also see some chunkier stuff too.
Of course if the pressure is the problem (rather than hard object pushing on joint) then the overgrip won’t help- it won’t change the pressure.
Last idea! Change to a wrist sling which would at least take some of the post shot stress out of the thumb?
I empathises as I get a nerve pinch that causes a bow hand tremor. It is bad with a high grip, terrible with a low grip and a bad with a wide grip. But a bog standard factory
Hoyt grip is usually OK. A Thinner grip is even better but not as comfy.
Stretch