When I started with various rentals 9 years ago I had similar problems. Then I got some Burton Motos and always after a few runs I'd be in a lot of pain with a burning/numb sensation especially bad in my front foot. Boots would sometimes be off on the side of the piste and for sure at lunch.
Only thing that helped was having them so loose I'd lose response. I figured that boarding just hurts when you only get 2 weeks per year.
Just before last season I picked up some Salomon Synapse and guess what? I could charge all day from first lift to night skiing with no pain. My legs gave out way before anything else. It transformed my riding and I can not wait until Jan 1st.
Not saying they are the perfect boot for you, just that the perfect boots are out there somewhere. I hope you find them.