Need suggestions My son has a flat spot on his head and we do tons of tummy time and holding and…

Need suggestions

My son has a flat spot on his head and we do tons of tummy time and holding and sitting and so on. He now rolls back onto his back and is not a fan of tummy time. Does anyone know of a pillow or head support that he can lay on that will help his head to grow normal again? I have an app this week with a specialist but I'm trying to get a jump start