You would firstly do well to add sizes to your bracelets etc.

And depending on thickness decide which size of tracked letter you need - ie 5mm for small - 20mm for large.

You’re a ‘free seller’ so you will have to use eBay labels. If you want to use your own postage methods, you will need a Pro Starter store, thus paying fvf….you need to do the Maths for what’s best for you.

As you're on the Free Selling plan, you'll need to use eBay labels  with the exception of items under $20 or those that can be sent as a tracked letter/envelope

Also make sure you're charging enough to cover your postage costs and and any extra insurance.

You can't post your $129  rings in a heavy storage  box as a large letter.

Australia Post is still the best way to send.  Others have bad reviews and can cause hassles. The buyer pays for Postage unless you have so called "Free Postage" which means you include the postage cost in the selling price.  Everything is expensive these days.