I can't tell you how sorry I am about your loss. I'm fairly new at chickens - first ones in July. So far, I have had five deaths, all for different reasons but this morning when I went in the coop I found my beautiful silver laced Wyandotte dead, I was devastated. She was fine yesterday, laid an egg and gone this morning. Who knows what happened? Chickens get so many diseases, injuries, etc. that it is hard to tell. I cried because she was such a sweet, calm chicken. No one understands how you feel about a loss of a chicken unless they raise chickens themselves. I don't dare tell anyone at work -- they always make some crude remark such as, "Did you eat her?"
I do heat my coop with a heat lamp that is on a bar at ceiling level and even a space heater at times. Chickens can't get to either of them. I live in Colorado and we have minus 40 below at times and even with my well insulated coop, I would not be able to sleep at night if there was not some kind of heat in there. I do let my chickens out every day and they will come out even if the temperature in zero and I leave the pop door open all day so they come and go.
There is a pretty safe heater called "Sweeter Heater" that is infraheat that you can mount on wall or ceiling. You can actually put your hand on it and won't burn, it can be cleaned and disinfected. It doesn't put out much heat but if the chickens stand in front of it, they will get warm and won't get burned. It will be great when the weather gets warmer - it will take the chill off in the mornings. Found it on line.
Good luck to you with new chickens - don't give up - they are too much fun.
Also from a fellow West Virginian.