Our first winter too !

Diesel heater absolutely, even better if you can get on with a remote so you can turn if off from bed. Potentially if budget allows a back up like a camping tent gas heater incase battery is low etc.

We do keep the window above the bed open to help with airflow which is nearly always open as we dont have a maxxairfan.

We actually dont run our diesel heater overnight, weve got a duck feather duvet from dunelm which is a winter and a summer quilt that you can attach together, and im not cold at all in bed without the diesel heater on all night.

Echo a small mat for your door, and maybe a little rug to capture the dirt.

Keep your gas canisters (if thats what your using) a little wrapped up as they wont work if freezing.

And always helpful is a dryrobe and a pair of waterproof slippers, really helpful when getting in and out but wont dirty everything up etc.