For a normal January day I will start with insulated underwear - what we used to call “long Johns.” New material is light-weight and very warm, and it will wick away any sweat so you don’t feel wet and clammy. Thin socks of similar material help keep feet warm and dry.
My next layer is a soft flannel or modern material long sleeve shirt and flannel lined jeans. Several brands make flannel lined jeans and you can order some from ads in magazines that are not expensive but are very warm. I top the thin sox with wool sox.
My fishing jacket is a baseball type lined jacket with a hood. It is water resistant and very warm, and the hood is great. I put on my baseball cap so I will have a bill to shade my eyes, pull a stocking cap on over it down over my ears, then pull up the hood. That keeps head, neck and ears warm.
If the day is real cold I wear insulated boots. If it is not too cold I go with walking shoes but try to make sure they are loose on my feet. If they are tight, especially with heavy sox, it cuts off circulation and actually makes your feet colder.
That is plenty if the temperatures range from the 30s to the 50s like it does most days. On really cold days I pull on a snowmobile suit over everything else and will put two to four chemical handwarmers in inside pockets. It is amazing how much heat those things put out.
If it is ridiculously cold, in the teens, I have Gortex insulated Cabelas Guidewear. These suits zip and snap up and with bibs and the coat you are covered from head to foot. The hood has a flap that snaps across your chin and mouth, covering it. For long runs I add a face shield and heavy gloves so no wind hits me anywhere.
I have fished in temperatures as low as 11 degrees and have been comfortable. My hands get cold, though. I have tried all kinds of gloves but none allow me to cast and feel the fish like I want so I always fish bare-handed. It helps to switch from a bait casting reel to a spinning reel. For some reason opposite hands get cold with the different reels so switching helps warm one. And one of the handwarmers in both side pockets allows me to stick one hand in there and warm it for a few seconds.
Dress right and you can be comfortable while catching fish, even on the coldest day.