Any boot is going to soften overtime, and you will be wearing out the soles, the buckles, and packing out the liners. Get a race style boot with rear spine rivets that is stiffer than you typically ski, and take some rivets out. Get the bootwork you need to make it fit well, and then ride them to death, buy new liners when they wear out, put rivets back in when the boot softens...
I have been riding the same pair of Head Raptors for a really long time...