I started using mine when DD was 13 lbs. I never bought the insert and didn't use a blanket or anything either. She is crazy tall though so that may have made her fit better length-wise. She did used to slosh around from right to left in the chest area. I just always kept one hand on her back whenever we walked so she wouldn't try to back-stroke leap out of it. (She moves non-stop and is hard to contain.)