I'm in a BIG KID seat too!

We had planned on having Ammon in the 5 point harness carseat until this summer when he turned 4, but then the cold weather hit. He couldn't wear his winter jacket under the buckles, and I'm not going to put him in the van without a jacket when it's freezing outside. His shoulders were at the level of the highest spot where the straps could come through-so he really had outgrown the seat, and lets add more-it had passed it's expiration date by way too long. We bought it for Simeon when he was 12 months old.
It was time to move on.
Ammon and I went out looking for a high-back booster today. We went to Walmart first. All their seats are strapped down on a shelf, but that didn't stop Ammon from sitting in them to test them out. What it did stop was me playing around with them. We found one that we liked-and it was on SALE. (I love that word!)

It is so much easier for us to buckel him in, and the shoulder straps stay in place really nicely. Simeon can even buckle it for us. Ammon can unbuckle himself-but he waits until I tell him he can. The back can come off when he's old enough for a backless booster-which won't be for a long time.