You need to find a quality boot fitter. Then it may take several days of riding and boot fitter sessions to get the boot dialed in.
A good boot fitter at a shop will start you off with the right boot for your unique foot shape and riding style. You'll start with the right size and go out and try it. Then you come back and describe in great detail what you're experiencing. You'll walk out with different insoles and/or wedges and go ride the next day. Repeat until things don't hurt and numbness goes away.
I did this with my fiance on her ski's last year. Her boots had worn out and were too soft. She was badly bruising her bone after a 1/2 day of riding. A couple of days was enough to bring her to near tears after a run despite constant icing at night and pain killers.
We went to an expert boot fitter and got new boots. New boots helped a ton, but were too loose in the toe and she had heal lift. She got an insert and went back out. Better, but not perfect. Heal wedges stopped the last of the heal lift. Came back to the resort the next week to buy the new skis she demo'd and verify the boot fit despite the fact that the conditions were awful. It took one more round of boot fitting to get the boots dialed in.
Modify and check. Repeat. It's no different than bicycle, saddle, and bike shoe fitting.
My understanding is that ski boot fitting is much more intensive than snowboard boot fitting. And that really wouldn;t fix anything because my boots are perfectly comfortable.
I guess I'll have to try lacing my boots differently to see if I can increase blood flow. I've ridden a few seasons with bad blood flow, so we'll see