What a purchase - timeless. I love your description of it too, especially the word "buttery"
I would recommend buying the skirt - it will be such a statement outfit and I can see you rocking it at a cocktail party (think luxurious jewellery and heels). Plus it will probably be as versatile as the shirt. Slip style skirts are so comfortable, relaxed but look luxurious.
I also like all the styles where it was tucked in, it is either the shirt or your body shape, but they all look gorgeous on you.
For the untucked outfits, I would try opening another button at the top, so that it opens more around your neck & chest. Also try wearing something contrasting underneath (while still partially buttoned). White is obvious, but you could do grey/silver or earthy tones too.