You don't need to change/add too much to what you have now to stay warm.

I have the Sitka Incinerator and Fanatic gear. The Incinerator bibs and parka are noticeably warmer. I basically live in them during gun season. I consider the jacket too loud for bowhunting but you might be able to get away with using the bibs. The clothes were definitely pricey but now I am glad that I bought them. I have some KOM and Gray Wolf Woolens gear and the Incinerator stuff is way lighter and easier to get into and move around in. It also packs down small which is a big plus.

Some cheaper gear is the Cablelas Standhunter parka and bibs. This gear is warm and quiet but heavy. You do not even want to think about getting it very wet.

Whatever you end up using for bibs and a parka I would want it too be windproof and at least water resistant.

For my hands I use the Gray Wolf Woolens mitts in XL with liner gloves. Inside each mitt I put an 18 hour handwarmer. I have lots of expensive gloves and mittens that now sit in the drawer. (For climbing up into my stand on wet days I wear cheap cotton gloves. Then I take them off in the stand and put on the liner gloves.) With this arrangement my hands stay warm and I can easily slide them out of the mitts.

For my head this year I tried a Cabelas Ninja Balaclava and it is without a doubt the warmest most comfortable thing I have ever put on my head. That includes the KOM and SI hats. I also highly recommend the Ravenwear neck gaiter which I pull over the Ninja. On top of the Ninja I put on a Raverwear Noggin Boggin. The XL fit is a bit tight so I am going to see if Ravenwear will make a custom hat in a larger size. Like others have said you won't believe how much warmer you'll be when you seal up your neck and head.

For boots I usually buy them a size large and stuff an 18 hour warmer in the toe box of each boot. Instant warmth.

The advice on puffy jackets and vests is also good. I tend towards using down vests.

Another thing I have found that helps me to stay warm is to use some type of seat cushion on my treestand seat when it is crusted with snow or ice.

I know most of my clothing is not cheap. But after many years of hunting I realized that buying second rate clothing in the long run was a waste of money if I wanted to stay dry, warm and comfortable.