I do exactly the same, a few of my own CDs and DVDs resold each month. I use Royal Mail then until this week had then picked ‘Royal Mail 1st Class Stamps/Franking’ and that worked perfectly. Everything arrives promptly giving me good Amazon feedback and my VTR is ‘N/A’. It sounds like I may need now to choose/type ‘Stamps/Franking’ as the shipping service instead. I’ll check on the next one I sell.
There really isn’t any demand for tracking on resold CDs and DVDs by customers. I’m a buyer too and there just isn’t any benefit on such low value and casual items. So at some point if I’m forced to use a tracked method or Amazon postage - I just won’t bother selling here at all after doing so since the start of Amazon in UK. I stopped sending outside UK last year and next it will be the end of being at Amazon at all I guess. I notice that the majority of sellers on CDs and DVDs seem to have disappeared from listings already.