The simplest is to cut felt shapes and sew them on - if you are feeling really adventurous you could make several styles - and change them about. I found a few example of this on Google images - just to show you what you an do.
I thought I would stay more traditional and add wool hair - so here's how too.
You can use any colour you fancy - or mix and match. I used cream, tan and a variegated browns. Wrap the yarn round something - depends how long you want the hair to be.
- and cut up one side to give you even lengths. Make a couple of inches at a time to keep it under control.
Lay the hair lengths across the top of the head - with a short length on the face if you want a fringe look. With a very sharp needle and thread - work across the yarns with tiny little back stitches.
Add another few inches of yarn and continue backstitching. You can add another layer on the top to build the hair up.
Lift the hair up - and add another line of yarn about half way down the back of the head.
I have not trimmed to neaten it yet - but it looks lovely and thick
And the back - needs a bit of a tidy but I don't have any sharp scissors on my lap
And I can't move now can I ?