Vantage wrote:2 pairs of overshoes. My smaller pair have a rubber like finish on the outside for water resistance and the bigger pair of normal neoprene overshoes just slide over the inner pair. Worth a try?
If it gets really cold I also use two pairs of overshoes. The inside pair are windproof with a slightly fleecy lining and the outside pair are neoprene. This set-up means my feet aren't squashed into my shoes as they might be with extra or thicker socks. A few weeks ago when it was -5 c I did a couple of hours and my feet were fine.
Also, try to make sure your feet are warm before you go out. Put your shoes near the radiator and you socks on them.