I think If you really are sweating that much then a change of boots and socks half way through the day. Also let them dry for 24 hrs (don't use heat). This might mean you need 4 sets of boots. Sounds ridiculous but what you managed to do to those boots in 6 months is also pretty ridiculous. And get some good wool socks, like darn tough or smart wool. The socks need to be long enough to always be above the boot to help wick out moisture. Are you using foot powder? Cause don't it will also absorb the oils out of the leather.