The JPMBB PhysioCarrier is designed for use from newborn to toddler. It has an adaptable mesh panel and comes with an insert for newborns (which can also be used as a booster for toddlers). It has a sturdy waistband and the straps can be worn crossed or ruck-style.
Here are the instructions for use with a newborn
There are more videos and photo tutorials listed on the Carrying Matters website.
The Sheffield Sling Surgery website is here - full of useful information about safety, all sorts of articles about warm/cold weather carrying. knee to knee support, big kid carrying and so on
Facebook page is here and the online support group the Virtual Sling Surgery is here