Talk to your physio when the harness is put on, we were actually recommended and encouraged to use a carrier like the bjorn's as it helped to promote the hip flexation that they were artifically creating for him. He found it a lot more comfortable that way then in the pram and car seat. So long as whatever carrier you choose to use doesnt squish their knees together (I think thats what she told us - its been a while) but definately keeps the correct positioning of the hips, you can use whatever carrier you and your DD find most comfortable.