I loved those pictures, but I'm not sure if I agree with the claim that these fashions were the kind of glamour worn by "supermodels" of the day. (Also not sure I agree with the idea they would have been considered "sexy" in the way most people use the word -- ballgowns would be more likely to get that term, I'd think.) The house of Worth -- who practically originated
haute couture -- was around in the 1860s. This page includes one of my favorites of his from around then, the white with green "Girl's formal evening dress, with, sash."
http://thedreamstress.com/2010/11/early-worth-gowns/
Also a fan of the orange ball gown on this page (I've found larger pictures of it before, but my google-fu seems to be off today...)
http://wilhelminamarquart.blogspot.com/2010/06/lovely-1860s.html
Not House of Worth, but another favorite dress from the 1860s:
http://thedreamstress.com/2018/04/rate-the-dress-an-enormous-pingat-ballgown/
I think many 1860s dresses are beautiful, but I cannot imagine having to wear one every day!