My gym is run by a Thai Master and although he has loads of pads, gloves, shin guards. There isnt a single head guard. I've never seen them used and there have been a few good fighters come out from here. You should only be free sparring when you're ready, the only reason that i see you having to wear head gear is if you arent ready and have to take unnecessary hits. A good sparring partner will be of equal skill and power and be able to spar with light touch. You build upto taking hits to the head in my opinion as this will be one of the hardest things to take in a real fight.