Welcome to EpicSki, Njadam.
For the most part, it won't be the socks that will matter. Wear wool socks, or synthetics, anything but cotton. But if your boots fit well, you won't have room for thick socks without restricting circulation and making your feet colder. Wearing more than one pair of socks can be even worse, as they'll probably just bunch up and cut off your circulation.
Boot fit is critical. Pressure points, especially over your instep, will make you cold. If you haven't had your boots professionally fit, it's well worth it--for this and many other reasons.
Some boots are inherently warmer than others, but the neoprene boot covers will make most boots warmer. They're not expensive. They're a bit of a nuisance. But they're worth a try.
You can also look into boot heaters. Several types are available, and they all work similarly. They involve a thin insole that heats up from a rechargeable battery pack. Old ones didn't work very well, in my opinion, but new batteries and designs are reportedly much better. I can't personally vouch for them, though, because I haven't used boot heaters in about ten years.
Most importantly, make sure you're dressed warmly in general, and that you eat a good breakfast that gives you some fuel to burn, and keep well-hydrated. If you lose body heat from anywhere, your body quickly reduces circulation to your feet, in order to protect your core and vital organs. The old saying goes, "if your feet get cold, put a hat on," and it is very true.
There is a common medical condition known as "Raynaud's Syndrome," in which the normal physiological response to cold is exaggerated and more easily triggered by cold and stress than normal. If you get cold hands and feet unusually easily, you might want to ask a doctor about Raynaud's syndrome.
Interestingly, your mental state can contribute to cold feet. If you just think it's cold, you may trigger the same physiological response as if you really are getting hypothermic. I have spent time with the Inuit people (Eskimo) on Baffin Island, and I'm constantly amazed at how they can keep warm in the coldest temperatures. They attibute it largely to diet (lots of fat!) and visualization. I asked one Inuit man who was particularly well-known for his tolerance to cold, and his first advice was to "think about warm things--don't think how cold it is." I was skeptical, but I've tried it, and it does work. It's pretty cool (pardon the pun). I should have known better than to question an Inuit's advice on staying warm!