You don't need the dimensions for such small packages. Just got a store, buy some 6x9 bubble mailers (size 0 I think is what they're called).
PayPal shipping is just more convenient and for US transactions, you can save a lot of money on delivery confirmation ($.18 at PayPal vs $.75 at USPS). But if shipping to Canada, it really doesn't hold much of an advantage as far as I know (other than convenience).