I know you said, "no boot-fitter" but how a boot flexes is something that can be very unique to the individual. For example, given your weight and range of ankle motion, the same boot will feel way to soft for one person but perfect to another yet to stiff for someone else.
This is where a boot-fitter will be very crucial for you- if you have a limited range of motion in your ankle (which you will not know unless you see a boot-fitter) you might try to buy a boot that someone with a normal range of motion loved. And it will suck for you.
So while it may not seem like non "go see a boot-fitter" question, it really ends up being one. How a boot will flex for a 200 pound person with no range of motion will be very different from a 120 pound person with a great range of motion.