I would go 'semi custom' if you can find a pair that fits your foot and lower leg well, but are to big on the top of the leg, take them to a shoe repair store and have them taken in.
I was amazed to find a pair of hardly used Effingham dress boots on ebay
, that are actually bigger than my calfs
I truly didn't know that was possible.
I'm taking them to have them taken in to fit me, when I get to a good weight
, but it will cost around $50. I will end up with a pair of boots that will fit both of my fat legs, and there is an inch difference between my good and bad leg, and for less than $150