Musts:
At least a 36 inch waist
Somewhere between midi and maxi length
Natural fibres eg. Cotton or linen, bamboo derivatives are fine.
Preferably:
Thick material with either structure or drape
One colour, preferably dark. Pattern or texture is okay as long as it doesn't look 'statement'y
Open to broader brand recommendations and/or fast fashion although I live in Australia so most fast fashion is not worth it. Most of my shopping is done on yahoo jp, but there doesnt really exist womenswear in my size there.