Iam a petite Mum of barely 7stones and 5ft1inches with a 18wk old clingy baby who hates his pram and screams when I put him down. A sling has been recommended but I am scared it will wear down my back. I currently have a Babybjorn carrier and it hurts after 15minutes. Will it be possible to use a sling without pain for a reasonable duration of time given my slight build? Any which you would recommend?