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You have said that your daughter is 4 going on 5. Will she be entering kindergarten in the fall? I know that you want a safe and comfy carseat, but when my children started school they began to see friends who rode in smaller booster seats and sometimes no carseat at all. My children are 6 and 10 and I still make my 6 year old ride in a booster seat - she really does not want to. She wants to be a big kid. Our state laws require a booster seat until children are 7 years old and meet certain height and weight requirements.
If your daughter will be entering kindergarten soon - I'm not sure that I would go for a big car seat. Just because she may soon see other kids her age riding in something smaller and begin to associate her seat as a "baby" seat and then it might be a battle to get her to ride in it. Especially if other kids her age are riding in the same car and are not riding in such a big seat. If that were to happen could you endure the battle and make her ride in her seat or would you opt to buy a smaller booster seat? Can you afford to buy more than one seat? I do not know of any booster seats that really look soft and comfy.
You have also said that you do a lot of traveling and that you are having trouble buckling the seat with her thick winter coat on. Would you consider a booster seat for her to ride in for short around the town trips, but use her current seat for longer trips when you could take her coat off while in the car.
If you get a booster seat consider one with big loops for the shoulder belt to easily pass through. We had one with a small area for the shoulder belt to pass through and our son would lean forward and then the strap would get caught and not go back into position. We would have to stop and pull the shoulder strap back. It was a big car seat that could convert to a booster - I quit using it as a booster and went and got a booster seat with a back made by Graco.
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After I sent my message this morning I was running errands and stopped in at Big Lots (don't know if you have one close) but they had a really nice looking seat made by Cosco it is an Alpha ? Apex 65 I believe and they had it priced in the mid 80 dollar range. It looked comfy and went up to 100 pounds and had a harness system and could convert to a nice booster. I think that it would be worth looking into. As far as carseats that convert to boosters it is one of the nicer more plusher ones that I have seen. When I just tried to look it up on the internet I found a similar seat that was made by Safety 1st named Alpha Apex 65 and it was close to 130 dollars at Target (It could be the same seat).