Without evaluating your situation, I can not give you an exact answer. There are reasons when you would use a cast such as a very large or very small individual who a cast boot would not fit well. Non compliance is another good reason. A cast boot is alot easier to put on and take off. If I have done a surgery, I can monitor progress, swelling, skin reactions, etc. For injuries, I can pad it as the swelling goes down. I can't do that in a cast. It is also alot more convenient to use a cast boot than to apply a cast. There is more work involved in removing a cast. Some insurances will not reimburse us for the supplies and work involved in putting on a cast and removing it.
Did you discuss your concerns with your doctor?