I dont know how those "Heater Body Suits" are cuz Ive never tried them, but for standard style of clothing, the bottom line "cold" hard truth, is no matter what you have on, when the blood pumping slows down (your movement), the heat stops coming! You can be wearing $2500 worth of wool head to toe....if you sit for a while with no movement, you are gonna feel the chill! Period! That being said, if its brutal cold, you can only sit so long with no source of heat. For sitting for a bit in temps just before the realm of stupid cold, I wear heavy merino against my skin, a hooded sweatshirt as a mid layer (try this, Im tellin' ya!) and either one of my Asbell zip wool hoodies or my heavier wool jacket from Autumn Wood Outfitters. I have to say also....unless its strangley warm on a day which happens from time to time, Im wearing wool bibs, also from Autumn Wood. The chest portion of the bib and back coverage are KEY to keeping the torso (your core) warm! The merino and regular cotton hoodie are under the wool bibs. Heavy merino leggings too, inside the bibs. I dont get cold dressing like this! And Id classify myself as a good sitter. Its always my toes that start to feel the cold first, after sitting several hours....and I have good boots, so thats when I know....gotta move a little, unfortunately.