I am confused when it comes to boosters lol. My son isn't ready yet but I plan on training in a year and full time a year after that(using his fn85 for that). The questions involve the booster I need to buy to start training him. I obviously don't want to keep switching his fn85 from harness to booster so I will need a dedicated booster. He will be 4 next month and has a 15 1/2 inch torso BUT in his nautilus he was on last slot with an inch of growth and his fn85 has I *think* 2 or 3 slots left. So my car eats torso slots. I was planning on getting a evenflo amp hbb but I'm not sure how high it goes. My other thought was a probooster but that's pretty pricy for a barely used seat. Btw my car is a 07 Toyota corolla and he is the only child(and will be for a LONG time). Any suggestions?