Headrest for Car Seat

One Step Ahead catalogue sells separate head rests for car seats. They have different kinds; Google them; their catalogue may be on the internet; you may also want to Google headrests for infant car seats or try EBay. Only you can assess what would work best for your child.

Chatula

We had to move my son when he was 6 months old into a convertible and his head did/does the same thing. He is almost 11 months old and it STILL does that when he falls asleep. We have 2 different carseats in each car, they each do that, and all of my friends have the same issue (they all have different brands) as well :( No advice, just wanted to say I think they need to come up with a better carseat!!!!
The only thing that does help is giving him a fluffy blanket or stuffed animal to hold onto and sometimes it holds his head from falling over.

I bought a headrest for my little guy that Velcros to the straps and kid of looks like to stuffed bananas. It holds his head in place from the top down the side of his head on each side. Got it at Babies 'R Us.

Check to see if your car seat has a lever to recline back. Ours (britax) did and that helped a ton. Sometimes tha back seat has a big slope to it. If you roll a towel to put under the carseat that might help. good luck. Also... take it to your local fire dept. They can help make sure it is installed correctly.

You see if one of the infant carrier head supports works with your convertible. I seem to remember that happening with both of my girls and thinking it looked quite uncomfortable. But, I never really did anything about it. Maybe I should have?!

If his head is flopping forward it is possible the seat may not be reclined enough.
I think 45 degrees is what is recommended for your son's age.
I do not know of anything else that could help.

I've read that although a floppy head might look uncomfortable to an adult, it doesn't really bother kids. If you want to try getting the seat to tilt, though, the officer that inspected ours recommends putting cutting a length of foam pool noodle and putting it under the seat. It works great!