In reply to BusyLizzie:
In terms of helpfulnessknowledge of staff I would go for Covent Garden Snow & Rock and then Cotswold.
I have bought boots from both and they have no problems with you taking time and trying on lots of different choices. Cotswold and (I think) S&N will also let you try at home for a limited period (provided they are not used outdoors) and exchange/refund if they are not quite right.
I have used Brigham but found them a bit off hand ( maybe I was unlucky) and they didn't do BMC etc discount though that may have changed.