I think, if you want to be relaxed and low maintenance, stick to clothes that are comfy, easy to pop on, like jeans and a t-shirt and some sneakers that you think are kind of snazzy. To remain feminine keep the t-shirt loose but close enough fitting that you curves are shown well, and cool graphic t-shirts I think are a good way to go. Also add a "something else" that you really like, something simple like a ring, necklace, hat, belt, or sweater that gives your outfit a little more style. That's how I do it at least.
Make sure even though your clothes are laid-back, they're fitted so you still look cute not like you're wearing your man's clothes. When I dress laid-back I try to wear my hair down and accessorize well.