Hello I'm Paige :)
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If you braid your hairs that are left into small briads, they will eventually start to dread on their own and it won't cost you any length. It may take up to a year for them to completely transform into dreads if your hair is straight and oily, but they will be a lot more uniform and you can choose the size. I think it will look a lot better to have half braids and half dreads than what is likely to happen if you just let the hair try to dread it'self. My hair is also straight and oily, so I also know that the oil will destroy the rubber bands after a while, but you can replace them, or use thin soft wire after they have started to set. You will still have to rip the braid/dreads to keep them separated, but you will have beautiful dreads when you are done.