Some time ago I bought a pair of 4 season boots, which are about 3/16th inch thick. They keep out the water, but weigh a ton and because the leather is so thick they haven't 'given' at all.
The problem I've had with water mostly is with water coming in over the top. For example walking in snow without gaiters - if your foot goes in deep, snow can be pulled into the boot as you draw your foot out. Others - rain can run down your legs, you stick your foot into that bit of ground that really looked quite solid ...
Fitting is always difficult and IMO always requires a trip to the fitter. You can't even assume that because one pair of boots fitted you the next range by the same manufacturer will as well. For example for years I swore by my Salomon boots, but then they started making them a size smaller for some reason.
However even a visit to the local gear shop doesn't always help, since it is nearly always the case that boots won't be replaced once they've been worn outside, so how do you know they'll be OK? Walking around the house isn't in reality a useful test unless you spend a day walking up and down the stairs.
My intention next time I need a pair of boots is to take a trip up to Richmond (Yorkshire) and get a pair put together by Altberg (
www.altberg.co.uk), expensive way of doing it but could be much cheaper in reality. I believe they even sell the boots mentioned above so perhaps you'll still be able to buy off the shelf. In know someone in the military who told me that many soldiers dump their army issue boots, get a pair from Altberg and buy a pair of Sorbothane inserts, and lets face it, they should know - I've seen them running up Pen-y-van with weights tied to their legs.
S.