Thermals help a lot along with ski socks!
LAYERS! You could also try a quarte sheet that wraps around you, they are also good for your horse!
I would wear leggings under your jodpers and tall socks layered and for your horse use a warm up blancket with your tack to keep them warm especially if it is berry cold ☺️
Ski clothes or onion layering. Ski clothes are much easier to move in.
Well in C I don't ride normally once it drops below -20 to -25 but I ride with a pair of leggings under my breeches, extra socks and winter tall boots, I just ride in regular gloves not made for riding and a scarf and this thin thing that I put over my head under my helmet that goes over my ears and part of my face to keep me warm.
I have a pair of cold temp leggings that I put under my breeches and have full insole foot warmers (disposable ones from Walmart) that go in my boots. If it’s too cold, I don’t bother riding. I also have ear things that fit in my helmet which are awesome.