Thanks Erin! You cannot imagine how helpful your comments are! I loved the idea of boat neck, fitted but not tight shirts, and leggings.
I already donated some of my old clothes so this weekend I’m going shopping!

Check yout this old post: http://www.collegefashion.net/inspiration/fresh-fashion-icon-kate-middleton/ for some inspiration. Speaking from experience, I would say that the hardest things to find in a “ladylike” style in stores are actually dresses — most are very short, very revealing on top, or both! But if you can find one, go for it, although it might be a lot to start out all at once.

I recommend picking up some layering tops — inexpensive plain t-shirts (not necessarily crew-neck; for a real Kate Middleton vibe, try a boat neck, maybe) and camis, and a couple of warm layers like button-down shirts, cardigans, or blazers. You don’t need a lot here, probably one basic shirt per day of the week and one of each of the top layers to start. Pick some tights to coordinate with your too-short bottoms for now, a pair of everyday flat shoes that fit your new style, ditto necklace or other signature jewelry piece (we’re talking like Claire’s here), and if you’re not all shopped out then, a nice car-length or longer coat. The length makes it look more sophisticated. These purchases will help you stretch what you have while you ease into your new look.

The CF article I linked you emphasizes that Kate wears a simple shirt and trousers or skirt for everyday, chooses clothes that are form-fitting but not tight, and strategically placed jewelry pieces to draw attention to her best features. She tends to wear a singlle color in an outfit, either repeated in different shades or with neutrals, so you might try that — with pink, if that’s a color you like to wear a lot of, just maybe a more subdued hue than hot pink… I also really like the suggestion to substitute interesting hair accessories (or a new haircut) for hats if you’re not accustomed to wearing one.