Thorogood Gen-Flex2. All leather with side-zipper. Found on Amazon.
BEWARE those that recommend anything that’s not all leather or considered military flight approved. Any of the nylon, polyester, etc. types of boots (under $100) will MELT to your feet in a post crash fire.
The military does authorize ones with Goretex sides, but they’ve been burn tested to confirm they provide “X” amount of time at “X” amount of degrees before melting. In my active duty days I got to speak with the actual laboratory researcher at the Army’s United States Army Aviation Research Lab and that’s what he shared (and then showed me the charred boots that were part of their tests (I would assume any of the military “Flight Approved” would be fine; not just Army).
That or any plain, lace up, all leather boot.
Watch the video from the Frisch crash and note how long it takes before fire entered the cabin area (and, yes, I know it was a non-crashworthy fuel cell).
It’s your feet and your life. Burn units are horrible places....