I'm very similar to Quickchange. It feels practical and does pretty well with playing, crawling, walking in the rain and mud etc, and still feels vaguely fashionable - well, if not fashionable then not something that I would feel frumpy in (and of course there's no such thing as actually being frumpy, just what makes you feel like you're badly dressed).
I wear either skinny jeans or short jersey skirts with thick tights underneath, with biker/work boots, and a variety of Breton type tops, checked shirts, nice sweaters. Most of it works together so there's no hassle coordinating. None of it is too expensive, to be honest, as that requires effort washing and ironing it, and I am lazy 
Thinking of it as a uniform. Find what suits you: skinnies, straight leg jeans, trousers, skirts and tights; sweaters, vests and cardigans, shirts. Then buy varieties on it. It's better to buy things that will work together and compliment each other than to buy too many statement pieces that only work with a particular skirt, for example. It might not feel that exciting to be wearing variations on fitted trousers and Breton tops, for example, but I can guarantee if those really suit you, you'll look better always wearing similar clothing than having variety in your clothes if some of those clothes aren't too flattering.