First, it's great that you address it now, while there's hopefully plenty of time to handle it without a helmet. My son had the same thing....
- we banned the use of any pre-formed chairs, bouncers, swings....
- do lots of tummy time.
- Also, after my son would fall asleep on his back, I would lean him more sideways, and use a rolled up blanket to help keep him positioned that way.
- The Bumbo chair up in front of some type of activity center is also a good trick to keep him off his head when he's awake.
Once your son is sitting up and crawling, it works itself out... so you just have to get thru the next couple of months..... In my case, I started to notice a difference within a week...