I too have cracked this recently. I have overshoes to keep most of the wind & rain out, and I wear one pair of thickish socks (woolen socks are ideal - they stay warm when wet) and loosened the straps on the shoes, especially the toe straps, to give plenty of wiggle room.
However, the real key is to keep your core nice & warm so that your body isn't trying to keep too much blood away from the extremities, and to insulate your head to avoid losing heat there. That gives a chance for the warm blood to get to your feet in the first place. For the zero-degree weather we've had recently, I've had thermal bibtights and a pair of kneewarmers for the legs, and two merino tops (one long-sleeved Howies under the bib, one Endura BaaBaa over the bib) and an Assos Airjack jacket. To complete the ensemble, Gore windproof gloves with merino liner gloves underneath. For the head, a Gore windproof skullcap with an Endura fleece headband underneath.
This sounds like a lot of faff, but it's only an extra layer over spring/autumn kit with some windproofing, and it's genuinely nice and comfortable at freezing temperatures - so much so that I've been enjoying my winter cycling just as much as my summer riding. The hardest part has been getting through the snow in our road out to the relatively clear main roads.
Of course today was really warm at 5 degrees, so only one merino baselayer was required and my hands got a bit sweaty with the merino liners. My feet were fine in a pair of hiking socks though.
Hope this helps,
Darren