Something doesn't make sense here because it sure sounds like your
boots are be too small.

(US) mens size 10.5 = 28.5 (mondo size)
(US) mens size 11 = 29 (mondo size)

26 (mondo size) = (US) mens size 8

Have a look he
http://www.snowshack.com/skiboot-sizing.html

I wear a (US) size 9 street shoe and a (mondo) size 27 ski boot.

If I were you I'd try a (mondo) size 28.5... if they're too loose find
a narrower fitting boot.

Try measuring your feet yourself. Simply take a metric ruler and
measure the length of your feet. The length of your foot (in
centimetres) equals your boot size. e.g.- 28.5 centimetres = boot size
28.5