Can anyone recommend a car seat

Hi,

my son is 4 and lives with autism. He is quite large for his age but has a graco car seat that was really expensive and extends to last until 12 years old. However my son has recently become agitated on 2 occasions and because he is in the chair with just the seat belt over him, as instructed by the manufacturer, he has leant forward n grabbed my hair from behind whilst I have been driving. I was wondering if anyone knows of any car seats that continue to use the 5 point harness system for children if his age or size. 

Thanks in in advance for your advice

claire