I have been through various of boots including Boom 80, Sundridge Hot Foot, Skee-Tex Field, Muck Boots Lune & Baffin Trappers.
The absolute key with footwear is to buy big enough to allow your toes to move & accompanied with some breathable wool socks.
Boom 80's & Sundridge Hot Foot are great value & warm, but not breathable, which results in cold feet over longer periods.
Muck Boots Lune - Absolute rubbish. Never ever again will i rely on neoprene lined boots to offer enough insulation. They simply dont & they dont breathe very well.
Skee-Tex Field Boots - I've had 2 pairs of these over the years. First pair i had were terrible. They just didnt keep my feet warm. I sold them on years ago vowing never again, however last year, armed with better knowledge on how best to wear footwear, i tried them again. The key is buying size overly big fo your feet. I have also read that people find these boots perform better with thinner socks than thicker socks. I have tried various combination of socks between 1 season & 4 season thickness & would concur that the thinner sock does seem to compliment these boots better.
Baffin Trapper - These ARE the ultimate thermal boot. Very comfortable, very warm (rated to -70 apparantly), completely waterproof and suprisingly lightweight. Not cheap at over £100 but imo worth every penny.