I've sent quite a few parcels etc. to Bulgaria using normal post office services. Anything I have sent 'signed for' has made it without a problem and have lost one send standard post. Luckily it was nothing very important.
On thinking about all this though would you not be better selling product you can buy in Bg, into the UK market? Rather than importing then exporting.
Another angle to consider depending on what you intend to sell is 'dropshipping' ie you don't actually hold goods just sell them on behalf of a company. They send them out & usually charge your credit or debit card before despatch. The margins are usually fairly tight on this kind of arrangement so you would need to be sure that your overhead was covered ie ebay & paypal fees, postage etc (plus profit of course!).