Hi! I also live in a Zone 7 climate, but high desert—we get relatively mild winters (weeks in single-digit lows, Farenheit) and hot summers (highs in the 110s F).
My young hens do fine with a good windbreak (I made tarp panels I can screw into the aviary) and deep straw to burrow in at night. When I have birds older than 4, I provide heating plates for them to sleep on. Mine tend to pair up at night anyways, sharing heat.
Here's a picture of my straw setup:
View attachment 4063039
And a depth reference:
View attachment 4063038
In my experience, Coturnix are generally more prone to being hurt by hot summers than cold winters. So long as they have A) a dry cage, B) a sheltered place to get out of the wind and weather, and C) an insulating substrate, they do really well in winter conditions.
If you ever notice them shivering badly despite your efforts, you could always add heat—I've used both ceramic reptile heat emitters and heating pads, and I like the pads better because the quail can safely stand on them.
I wish you and your birds success!