I.V.
Seats are usually based on weight. Most toysRus or similar will do a fitting service and will weigh the child. At a a year, they are normally too small for a high back boaster with just a seatbelt and need better support. We had Graco seats after the small baby carrier and my girls were in these a few years till they transitioned to a high backed boaster with just a seatbelt. Have a look on line, as always a help and will give you weights for each seat.
Hope that helps.