I realize this is a bit of a spoiler, but I've written a handful of chapters that included Cassandra's "siren" outfit that her and her friends wear on certain occasions and as a group to the fetish club, etc.
I feel a bit guilty in a "typical male" sense whenever I do things like this (or the blatant bi-sexual cuckolding, etc.) but it's tough to keep going with ideas... and it's a lot easier when they happen to fall into my fantasy wheel-house, even if they are typical.
The baseline for that outfit is something along the lines of:
Staying true to me (and how I have written the characters) it is of course, fur-trimmed. I know that I have described some of the features more than the actual look, but if I (try and struggle) to remember how I have written it, it's probably closest to the far left and then accessorized in various ways to form a completed ensemble. In my mind's eye it could probably be any of the three. A key feature of the written version is that it has a removable crotch that allows the wearer to have sex, wear a strap-on, or receive oral pleasure without having to remove the entire outfit.
I do know that the concept of a "Domme uniform" is something that many newer Dommes find daunting or intimidating. The fantasy/porn side of Femdom has pretty much established this as black leather or latex, tight fitting, lots of exposure, etc. which doesn't always mesh well with many women.
I have given a lot of advice to newer Dommes over the years on this subject and I will echo it again here. I believe that the best "Domme uniform" for her is whatever makes her feel the sexiest, most confident, and most attractive. Those are some of the feelings that foster dominant feelings and whatever clothing (or lack of) brings about those feelings is the best choice. This could be a business suit, a certain type of lingerie, a favorite outfit, and so on... it can take any shape and form as long as she feels good about herself while wearing it.
As Cassandra's outfit will likely make an appearance soon I wanted to write more about it. Since Cass tends to be dominant no matter what she's wearing, this is just for special occasions.