Don't put your hands behind your head. That will only partly help, as you'll still tend to want to 'lead with your head', but with your hands there, you're just pulling your head up first, leading to that neck pain.
Planks are a superior move, so by all means consider switching your move! You have problems with crunches, so don't do them.
If you do insist on crunches though, keep your arms crossed over your chest, keep your eyes on the ceiling directly above, not your own knees, and try to think about your neck and keeping it 'neutral' while performing the move.
Deb, in New Zealand