You can latch baby to sleep or just carry her. They need the security to let them fall asleep. Another way is to swaddle her. I have a few friends swaddling their babies to sleep and it is known that babies tend to sleep longer when swaddled.
If you are using an ergonomic carrier in the right way, there should be no worries on their spine development as it caters to their body. My baby have been using a carrier since 1 month old and he is 8 months now.
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