Both my girlfriend and I have bought Lenz heated socks to try and stop our toes from freezing. After buying ski socks that cost ten times what a normal pair of socks costs, they still expect you to pay for the app to unlock the highest heat settings. Furthermore, the socks are very thick and may not fit into your boot if it is snug. Finally, they do not heat up your toes. The balls of your feet get really hot, but your toes may still be completely frozen.
Maybe if your boots are looser the heat will be able to transfer better?
I am not sure if SIDAS heaters are a better solution for tight fitting boots.