The French Revolution began in 1789. A Midwinter Night's Revolution begins, therefore, in 1786. Fashion in these days (as far as I can tell,) was dominated by the excesses of the French royal court. Some of the fashions, therefore, were very silly--like the enormous wigs. Others were lovely, if impractical. Regular people, of course, wore much simpler clothes.
Lyta's nicest dress, the one she wears to the second masquerade, is in this style: Felicity's work dress, though hers is brown with yellow stripes and a pattern of yellow flowers. For normal affairs, she might wear something like this quilted dress, or this striped dress.
These are quite distinct from the multi-part affairs like this robe a la francais or this Italian dress. (These are close in style to the one commissioned for the third masquerade, especially the square collar and ruffled cuffs, but hers was simpler, with only ribbon embellishments and no embroidery.) Lyta would have never worn anything like this or this, except perhaps during her brief stay at the faerie court, when her own clothes were ruined.
To be frank, Lyta's father would never pay for a fancy dress unless it had some purpose. Lyta has more affection than her father for "frippery", but her lifestyle is much too active for such things, though a top like this Spanish vest might certainly turn her eye, or this Polish (or Polish-style) dress. This this absurd court dress, though, she would regard with nothing but horror.
Jasper, by contrast, wears extravagant things without a second's thought. Luckily, it was an age when men wore beautiful things; shortly afterward, men's clothing became much less ornate. Fashion in Jasper's world is a bit behind Lyta's world and they have different collars, but he is always keen on the latest human styles.
Just as with women's clothing, there's a clear difference between the clothes worn by the wealthy and the common. Another men's jacket. Jasper, of course, likes his jackets decorated with jewels, but the gold embroidery make a nice accents.
The dressing gowns I've found surprised me--I expected something more like a modern robe. I enjoy their emo-style, but I can't imagine Jasper buttoning his all the way up. Here's one in a more decorated style.
And finally, the interior of a carriage--add some magic lanterns, four terrifying dragon-horses, and a set of goblin footmen, and you're ready to go.