You can't go to far wrong with mid-calf length boots with a low heel.
If it's cold wear them with tights or jeans tucked in, if it's warm bare legs. As long as you have a brown and black pair, and belts and bags to match, you are pretty much set for anything.
Of course you will decide you really need more than one pair of each, and more than one style, and a pair with a heel would look sexy, and.....
If you don't believe me, look in my wardrobe

Karen.