registered post is the way to go , however even this is not without difficulties.
a tip to senders that if you pre-purchase registered post rolls of 50 you need to keep your receipt as well as offer proof of postage (basically i still purchase the stamps each time i send a package and also keep this receipt)- australia post will look for ways to deny your claim if the package is lost without documentation.
also recently had a case where a registered item was sent interstate but did not arrive after 3 weeks, rang aust post and it was finally located at the interstate sorting facility so im not surprised at the experiences other members have had