Living and working outdoors in Northern MN, I consider myself a connoisseur of sorts when it comes to cold weather gear in general, and especially footwear.
You're on the right track looking to a waterproof rubber boot and wool socks! I'll give you a few levels of cold/wet, and what I wear. Rationale will come at the end so I don't bore you.
All levels of hot and cold: ALL BOOTS Lacrosse 6mm wool felt insole. Lose the gel pack and OEM garbage. Heavy wool felt under your soles is the way to go. There are a few kinds with foil looking stuff in them. They work well too, make sure they are sufficiently thick for cushion and to insulate the part of your foot that has the most contact with heat sucking ground, snow, ice, etc.
Mild cold down to about 20F and relatively active, sedentary to the mid 20's: Wigwam cotton boot sock, Generic "medium" Merino wool sock in uninsulated boots. This is my standard late fall work or walking setup for leather or rubber boots.
Medium cold, down to low teens and sedentary activities to 20F or so: Generic silk liner sock. Heavy, lofty wool/acrylic sock. Oversized boot with some insulation value to the boot. My standard "deer stand" setup in moderate cold, with a Kamik 800 gram under-knee rubber boot. This is grainy snow territory in MN. The crystals seem to get everywhere, and the extra loft provides some protection.
Deep cold, to 0F, single digits for sedentary activities: Silk liner sock. Heavyweight Alpacas of Montana Alpaca wool sock. Worth every damn penny! Boot with significant insulation value. I wear a Viking logger/lineman boot for this application. One could do well with any of the Baffin or Kamik felt and thinsulate rubber pac boots if they didn't need the extra PPE for work. They're $250 rigger boots, so I give them a dual life for work and play.
Severe cold. Below zero, sedentary activities...good luck!: Same as above, but I'll add an Angora (rabbit wool) ankle sock over the silk layer if the boots allow enough room to not be constricted. My deep cold boots do. I've found nothing that will keep my feet warm in sedentary activities near or below zero for more than 1 hour. I try to avoid sitting still at those temperatures unless it's napping by the wood stove at camp or sitting in the sauna. This level of cold is no joke. Be sure to have a fire kit and know how to use it. You can lose toes before your vehicle heater throws enough heat to keep frostbite from setting in. Pro tip, use the exhaust in an emergency, it warms up far faster than the heater.
Rationale: Everybody's feet and circulation are different, so your results may vary! The biggest risk to cold feet constricted circulation. Second is sweat and the inability to wick it away. Silk and cotton are excellent at wicking water, and silk has the bonus of a very high R value by weight and thickness. At warmer temps, I'm more concerned with my feet being too hot, hence the use of cotton and thin wool there. At around the 20F mark, I start desiring more insulation value. I find the lofty generic wool/acrylic socks in a loose fitting boot to be the answer here. Air is a fine insulator. Any colder, I break out the big guns in the expensive Alpaca socks, which are heavy and quite lofty. Alpaca and Angora are superior insulators to sheeps wool. If I could find Yak wool or a goose down sock product, I'd wear it. That's better yet. Don't constrict your circulation! Any tightness in your sock wear and you will have cold feet. Hope this helps!
They've come down in price since the last time I bought them. Don't let the pretty ski-bunnies and sad hipsters in their adds fool you. These socks are legit on the pipeline and the deer woods too!
https://alpacasofmontana.com/collections/hunting/products/alpaca-arctic-socks-warm