I do have poor circulation (gone through all the auto immune tests etc). Although it does affect my hands as well, the game changer for me was Winter Cycling Boots - I have Northwave Raptor GTX. I got them for gravel biking, but they’re so good (but expensive) that I swapped to spd pedals for the winter road bike too.
I either use Galibier Firefeet socks or I have some ski socks. I actually tend to go for the ski socks (under tights) as they go to just below the knee.
The other thing I’ve been told by medical professionals is that keeping my core (or trunk 
) warm will help my hands and feet circulation in cold weather. If your core is cold the body concentrates blood flow there, apparently.