Although I gave up selling on eBay years ago when they ditched PayPal as the default means of sellers receiving payment for items that they had sold, there is one option that you could try which I often used to do if I sold a lot of items around the same time. It always helped me to avoid mixing up the parcels I had to get despatched, so perhaps it'll work for you as well should you care to try it out.
What I used to do if I sold more than one item at around the same time to different buyers was to get out my selection of Jiffy bags, work out which size bag was needed for each item (or buy a suitably sized box at the Post Office in the event that a Jiffy bag wouldn't suffice), write the buyer's name and address on the front and put the eBay listing number on the rear of the Jiffy bag (or on the bottom of the box if I was posting the item in a cardboard box). Once I had done that I would use an Excel spreadsheet to make a list with four columns on it and as many rows as was necessary, fill in the relevant details and then print it off. Each horizontal line represented each separate item sold, with the various details listed in the various columns. Column A was the item that had been sold, Column B was the name of the buyer, Column C was the listing number and Column D would remain blank for the time being. More on that later.
Once I had done all of that I would print off the spreadsheet and take it, along with the parcels/boxes down to the Post Office, get them weighed up as necessary and then, before despatching them, I would stick the tracking labels on the parcels/boxes one at a time. At this point I would manually write the tracking number in Column D next to the listing number in Column C that appeared on the back of the package I was dealing with, then once I had done that with all of the parcels/boxes I would drop them off at the self-service hatch where the items were to be placed once they were ready to be posted out. (My local Post Office is largely self-service, although there are still some manned tills remaining.)
Finally, once all of that had been done, I would take the completed spreadsheet back home with me and enter the tracking item against the relevant item on my Sold page, then I would draw a red line across the line that corresponded to that particular item, continuing in this manner until I had entered the tracking number against every individual item on the list, using the details in Colums A - C to ensure that I had entered the correct tracking number against each item on my Sold Items list. To some people working through things in this manner may seem like a bit of a faff, but I can truthfully say that all of my items found their way to their respective buyers and I never seemed to struggle with working out which postage label was to go onto which parcel.
In addition to the above I also always used to write "If undelivered please return to..." followed by my name and address on the reverse of the package/box, just in case the item could not be delivered. I was fortunate in that I never had an item returned to me owing to non-delivery, but it pays to take precautions against this type of thing, just in case something goes wrong with delivery of the item.
Sorry for the long post - I'll shut up now and leave you to decide whether you wish to take my advice!
