If your legs swim in the shaft (top part) part of boots, you can always have them taken in. An old school shoe repair person can do this for you. The process is similar to tailoring clothes.
The above pair of boots were modified to narrow the shaft by Gino at Anthony’s Shoe Service, Union Square, San Francisco. Well worth the $80 cost of getting a perfect boot, calf fit.
If you have trouble finding boots that fit snug, a talented shoe repair person, can be your new best friend. Ask around, chances are there is just such a person in your City or Town.