I guess you could dress with some fitting jeans, tank-tops (it's not too far from the 'sporty' clothes but usually looks way more feminine), and maybe a light blouse on top of that. Once you get used to that you'll probably be able to shift to different kind of tops and so on.

Remember to always wear something you feel comfortable in. It might take some time to find that, but don't force yourself, because you'll end up feeling weird and uncomfortable - and that will pass through to your attitude. This is also the best way to disgust you with a style. It's better to go progressively.

Also, the change might be less radical - you probably won't have that many people to say to you "oh, you changed your style" suddenly, but you can be sure they'll notice it eventually.