I see where you need to either make/get a bigger coop or get rid of some of the flock but what really worries me is the ventilation issue. You do need to get them more ventilation, I would hate to see them suffer from the issues that comes up with that. I use the straw for the DLM along with DE. There isn't an odor and it stays dry in the coop but I do live in the desert and it's very dry in Summer but we get snow in Winter and very cold but not as cold as you. So, you can keep the straw until you run out and then go to shavings if you want but Good Earth recommends straw for the coop due to it trapping heat in it.
I like your coop too.
I like your coop too.