To the poster.   I raised a topic on auspost site a couple months back re the buying the tracking number esp for this sitution as we too were using padded bags for some of our smaller goods that fitted into the DL pricing.    Even  suggested that AP look at a pre paid padded bag range with the tracking the same as they DL range.    

AT the time the reply from AP was THEY ARE going to be releasing a PADDED BAG DL letter range soon with the tracking for the gap.    Guessing it will be the new year NOW with covid etc...

Atm we are using the DL tracked letters with a padded bag inside them as a get around.