If a buyer is displeased about an extra $1 on postage and your paying extra for packaging I would include part of the postage cost into the price of the item, for an auction though it can't really be done at a 0.99c start price.   Maybe look into flat rate postage like 'click and send' boxes and satchels and the normal ones available from the post office so that you can give a price to start with.   The flat rate boxes are quite good for heavy large(ish) items although I am still unsure if they can be registered or "signed for" or insured.

Yes you can add Signature required, and extra cover when required to C&S, which is now the equivalent of registered post.   but for proof of postage only, you are not required to add signature required with C&S to satisfy paypal.