Portable thermal printers are cheap, easy to use and if they break, they don't cost a fortune for a decent replacement.
This page will generate a PeriPage compatible document out of an A4 PDF generated by Royal Mail Click+Drop (or returns etc)
Once a PDF is added an image should be generated below which can be saved to your device and then opened in PeriPage app and printed. Using A6 printer with 206 dpi on medium settings works perfect for me.
PDF don't work? @ me on twitter and be prepared to send ur pdf