My wife has the same issue. I’ve ordered a mixte steel frame from Handsome and have the same concern that it might not be low enough. I’m hoping to build it around 25lbs.
A true low-step and low weight might be tough as well as incorporating the S&S couplers.
I would try to search out mixte frames or bikes before the Expo to get an idea how low the top tube has to be and then talk to some builders. Also get the geometry of the Seven and see how close you can get to a similar ride.
John