Doing a fair amount of driven hunting, and spending hours standing motionless in the snow, at as low as minus 14c, you soon learn what doesn’t work !
I find that if I keep my feet warm, the rest stays pretty warm too.
I bought some Therm-IC heated inner soles. I make sure my boots are warm, and dry before putting them on, and switch the heat on low, straight away? Just to get things warmed up, but preventing sweating.
Marino wool base layer, down filled trousers, in the Sportsman sale, £50.00, reduced from £ 200.00

thin fleeces I can add or remove as required, decent waterproof coat.
I’d try a heated top, but I’ve yet to find someone prepared to carry the 12v car battery for me