Combination harness to booster car seats

Mommas, I am starting my search for the forward facing harness to bolster seat as we have a 3 month old now too and we will be passing down the convertible seat to the baby as soon as I can’t lug him around in his bucket anymore. I am starting the hunt now so I can find one for a good price as I will need to buy 3 🤦🏼‍♀️ one for each car he rides in. What are your favorites? Which ones don’t push their head forward to prevent head drop when he sleeps (if only that would ever happen) any suggestions?