very large bubble bubble-wrap might help too - help to cushion the knocks - and also make sure that you mark your packages as Fragile. I have Fragile tape - big red letters on white tape.
Btw - if you are already listing these items, please make sure that your postage and packing charges allow for the weight of the box and the packaging materials, as well as the actual postage. Postage rates change if the box is that large and weighs over two kilos. You might be better going somewhere like WH Smiths and sending it via DHL.
I mention this because I sell on eBay and always weigh items in their intended packaging, when calculating the P&P costs - I got caught out badly at the beginning where buyers paid a lot less postage than it actually cost me to mail, so overall I got less than the sale price for the item.
I was in the queue at the PO yesterday when a woman was trying to mail a parcel containing a small suitcase - over 2Kg, to an EU country. She took it away again when she was told that postage alone would be £28....