One other thing that will help more than you think is to start with a DRY pair of boots. After a day or so of hunting, there is significant moisture trapped in your boots. Part of your heat will be going towards heating that moisture so it can evaporate out.
The PEET boot and wader dryers will solve the problem. You can normally find them for less than $35. They produce warm, but not hot air, and don't hurt the boots or waders in the drying process.
I use at least one size larger than my normal boot size for my cold weather boots and I have notices a major difference since I went that direction. If your feet are tight and cramped in the boots, your circulation will be impacted and it is almost a guarantee for cold feet.
If you are having a real problem, the boot blankets do work. They are something extra to carry in and are cumbersome on the stand, but they work. Add a handwarmer to each boot blanket on top of your toes and your feet won't be your weak link.
And, one more item that isn't on your feet that will make a major difference is a neck gaiter. I use one by Buff that has polar fleece covered by one of their camo buffs. It is amazing how warm the thing is. One of the factors for cold feet is that the body "steals" blood/heat from the extremities to keep the core organs warm. If the rest of you is warm, the extremeties don't lose out as quick.
I just bought another Polar Buff this week to have a spare in case one got wet or lost after wearing one on some cold IL days.