I absolutely say that boyfriend cardigans are the way to go. I love them so much, and they take up a huge part of my closet. Stripes have also been popular this season. I really like them. Rings can also add edginess to any outfit (Polyvore has some sickkk rings! Like the back bone/spine ones, and tons of awesome skulls)You can pile them on, without looking trashy. I like BIG rings a lot.
Also, you can still look edgy and casual while wearing a skirt. High waisted skirts are in right now, and they should stay that way. they're just a lot more flattering than skirts that hang on your waist... You can add a cool vintage shirt or Band t shirt to a high wasited A line skirt. I saw the grey skirt at H&M and I LOVE IT! However, it was a little too spendy for me... Anyways, be careful on what t shirt you wear. Some of them look weird with A line skirts. BERETS!!! they're so cute, just beware, those sparkley ones are kinda tacky...
I really like the boyfrien blazers too! Just because they are "preppy" doesn't mean you can't add things to it to make it edgy. Black skinny jeans would also look good, and maybe even those shredded ones too. Jewelry can pretty much make an outfit, you can add studded cuffs or edgy chain
I would like to add that you can stil wear florals or pink, and be "edgy" I do it... here, Lemme show you [: