There are no "safe, aftermarket" headrests.
The headrest on any vehilcle should not contact your head during normal driving. If it does there's something wrong, and I suggest you investigate the reason you're having this problem.
"Headrest" is not the best nomenclature for this device. It should probably be called a "head restraint," to function in case or a crash.
If you're using the head restraint as a head rest I don't know what to say. You shouldn't be resting your head while driving.