I'm in TN so our winters are rarely below zero, heck anything below 10-15degs is COOOOLD & when we do get such temps they rarely last more than a day or two. But on those rare occasions we get much below 15-20degs, I have something that's kinda like a "3/4 length" heater suit. I've had it for years & rarely use it but when I DO use it, it works quite well. I cant even remember what it's called but essentially it's a thick, heavily insulated, mossy oak camo, goretex "chest length sleeping bag". It zips all the way down the front for getting into, once you climb in it you zip it up & it also has shoulder straps to keep it up around your waist while seated. It makes a big difference! I let my kids use it when they were smaller & didn't have as good of cold weather gear as they do now that they are big enough to wear mine.
As I understand the heater suits are so thick/warm you don't have to wear your regular thickest/outer layer like a wool or down parkas while on stand? IMHO that WOULD be nice as I usually don't put my parka/coat on until I get into the stand & actually sit a few minutes to "cool off" after the walk in. Just a set of thermals, my beloved chamois shirt & regular weight hunting pants plus a heater suit would be nice to have on once in the stand.
My best friend & hunting buddy lives here in TN but he's the Exc. VP of a giant steel company based in Can & he travels up there at least 2-3x a month. I keep telling him we MUST get a Canadian deer hunt planned before we're to old for the weather. You CAN BET I'll have a heater suit or something similar for an all day sit in the woods in those frigid temps!
Sitting 2-3 hours on stand in frigid temps is one thing but sitting there 4-6hrs or even all day is another thing all together!