What she said! WEndy is our expert.
Just in case you need another person in agreement, there isn't a single seat that will rear face, forward face, and then be a backless booster. Also, there isn't a seat that does rear, forward, and then booster that is good at all three of those. Generally the thought is jack of all trades, king of one or none. Seats that try to do too much so far have not done great jobs at all they try.
You want a seat that will keep your child rear facing as long as possible, to at least two years old, but preferably longer if she still fits, and then will harness forward facing until she's at least 5 to 6 years old.
AFter that, you will want a booster WITH a back, not a backless. Particularly in case the child must ride in any older vehicles that do not have adjustable headrests in the back. You always want every person in a vehicle to have head support at least to the middle of their ears.
After your child outgrows, by height, a backless booster, then if they still need a booster you move to the backless part. Most boosters turn into backless. Kids need boosters until they are 8 to 10 years old, 80lbs, 4'9" tall, and pass the five step test.
Wendy mentioned it, but it's important to note again that car seats and boosters do expire. So almost any seat you got now would expire before your child was done with it if you tried to do rear, forward, and then booster with it.
At the store you will see Alpha Omega, Eddie Bauer, all-in-one/three-in-one seats. Don't buy it. It's an expensive seat that doesn't live up to its hype. It's not very good at rear, forward, or boostering.
Convertibles to check out:
-Evenflo Triumph Advance 65
-Graco MyRide
-Diono Radian (they have three different models, all essentially same, different price pays for different bells and whistles)
-The First Years True Fit
These seats will last a long time forward and rear facing then you'd buy a booster.
Also, there's a review section on this forum that should have reviews for some, if not all, the seats listed