If your primary concern is moisture transfer, will a full leather boot be breathable enough when pushing hard? Trad cycling shoes usually had holes punched all over them for a reason.
Those Reynolds boots aren't cheap, but by the standards of hand-made-in-England etc etc. they're not ludicrously overpriced. Might be worth giving William Lennon in Derbyshire a call? They still make leather boots and trad cycling shoes, and will do custom orders - I suppose it will depend on whether they can get hold of suitable soles (I note the Reynolds only come in sizes 8-11, which make be a sole availability issue).
Otherwise this may be an impossible ask for cycling-specific gear; what do winter cyclists in Scandinavia do - flat pedals and regular winter boots?