Yes an internal mesh door in addition to the normal shed door. I’ll add pictures of my shed and its mesh door.
Both the outdoor door and internal mesh doors are stable style so I can have it fully open or half and half. My shed was custom built but we made the internal mesh door ourselves (it was cheaper!)
My window doesn’t open (annoyingly). If it did open then it would also need mesh inside for protection so nothing to get in with the window open.
I don’t have electric in my shed so no heater.
Oh, just realised I’ve deleted the pictures off of my phone
- this thread of a conversation I had with another member contains the photos of my shed door
How to make inner mesh door on playhouse