I bought a Bjorn One carrier yesterday. Tried it on briefly in the shop and it seemed fine. Put it on for ten minutes when I got home and my lower back is breaking! Googled for solutions and the consensus seems to be that Bjorn carriers are uncomfortable and also unsafe for baby's hips.
I'm debating taking it back to swap for an Ergobaby 360 which apparently is "hip healthy". Any opinions on either carrier?