Back in my teenage days, when I was growing out my hair after dissolving most of it with a relaxer, I used to sleep in a bandanna. I was in the dorms at the time, and had a roommate with straight hair. Whenever she came into the room after I'd gone to bed, I'd hide my head under the blankets so she couldn't see it on my head because I didn't want to even go into what was going on with my hair, the relaxer, the relaxer disaster, and why I was using a relaxer in the first place.

Now that I understand my hair much better, I say that for sleeping, if you have very short hair (too short to put in any sort of buns or braids) you could just sleep in it loose for right now. Your hair will either rub against the fabric of the bandanna or scarf, or against the fabric of your pillow at this point, and they both seem almost the same. Satin pillowcases are an improvement, but your hair will still rub against the fabric. However, since it's so short, this isn't a big deal because there isn't much length to the hair to get damaged or to rub together anyway.

When your hair gets longer, you can then put it in several buns at night, maybe about four (two on each side, one near the top, one near the bottom of each side). This will protect your hairs from rubbing together, or rubbing against the fabric of the pillow or scarf as you sleep. So it will also cut down on tangling. But for now, since it's so short, tangling won't be as much of an issue as it may become when your hair gets longer.