For short hair, you can keep the brush head small. With fine hair of thin or medium density a Handy-size brush is all you need, either 100% boar bristle or a mix. Though your hair may be fine, if it could be described as "fine, but a lot of it" get a Bristle & Nylon model. You will need the stiffer nylon bristles to get down to your scalp.
You could also consider a Pocket-size model. They work just as the equivalent Handy models do, just requiring more strokes to accomplish the same result. But unless cost and/or compactness are important, get a Handy. Unless your hands are small, it will provide a more satisfactory grip.
If you prefer a larger head, the medium or large versions of the recommended brushes will work fine too.
If you haven't yet had a look at our full Brush Guide, we recommend doing so.