I love your idea of a velvet coat for the opera! I also love Brooklyn’s velvet coat. If & when I ever get going to second hand stores, it sounds like a long velvet coat is something to keep my eyes out for.
Other things that cross my mind occasionally but are not needs:
A cocoon coat that goes to tops of thighs in a false plaid menswear pattern, mostly b/w, but with a stripe or two of green &/or pink (but not in a preppy way)
A white teddy bear jacket, maybe long enough to cover my butt, or maybe cropped—but white, unlike this find.
A girly looking winter coat in pink or purple with ruffles.
I wouldn’t turn down a fun, bright-colored plaid coat or a velvet puffer if they came my way.
Winter coats I own (in order of warmth)
Big blue parka with black faux fur around hood
Dark brown aviator jacket from LLBean with thinsulate lining
Knee-length wool coat
ETA new blue “varsity” jacket. I think this is where it fits in, warmth-wise, but am not sure yet.
Black leather motorcycle jacket, oversized
Red puffer, short (but not cropped) tied with black leather jacket for warmth