I recommend FilliMilli hair rollers for root volume.

The first thing I do after drying my hair is roll it up. Lately, I prefer to add volume to my roots, so I always use FilliMilli hair rollers to secure them. If you apply a little heat with a hairdryer before taking them out after you've finished your makeup, it helps extend the hold of your hair, which is great!!! They are also quite affordable at less than 5,000 won for two, and since they are convenient to use and easy to carry around, I highly recommend FilliMilli hair rollers^~^