Thanks for chiming in, everyone - I'm leaning towards ordering the US8.5 not 9, if it should be able to accommodate insoles...
@Suz Thanks for the detailed advice! I do live in a subtropical humid climate, but my plan is to wear these in the winter. Whilst we may not get much winter rain here, there's still the odd puddle & errant AC drip to be aware of outside Plus I'm sure they'll get even more use in the UK - I'm not from too far up north in England, so don't have to worry about thick snow (from the top-down Nordstrom photos, it seems as if the side zips have leather panels behind them - so I suspect they'll be a bit more water-resistant but of course not fully snow resistant).
@Angie How do you determine if you have long vs short toes? Pointed toed shoes often pinch, but I suspect this is due to my wide forefoot rather than my toes...
@Firecracker Thanks - city walking will be my main activity here! A waterproof tall boot is also on my list, but I think I'll need to try those on in person since I have annoyingly in-between calves (16" calf circumference - so neither 'straight' nor 'plus' sized, lol).