Definitely going to echo this point here. Far too often I hear skiers asking for a "softer boot" when in fact this can cause more issues than solve. If you have a limited range of motion in your ankle, then a soft boot will do nothing to help keep your ankle in place. If the boot is allowed to move more than your ankle is, it will allow your ankle to flex past its usable range and cause some damage.
Do yourself a favor and see a boot-fitter who will perform ankle flexibility and range of motion tests. He will then find a boot stiffness that matches your flexibility so you will have a super comfortable and supportive set up.