In reply to neuromancer:
Look at your feet and ascertain any difference between the two if you can (split foot into three; front middle and back, and look at width, height and volume paying special attention to the heels). If you can find any differences it will let you know where to focus your attention.
If the heel is smaller use a heel-lift under your insole. If the volume is less you could try a volume reducer, these can be used whole or cut in half if needs be, and place under the original insole or superfeet if extra volume reduction is required. If the volume is lower around where the arch is located try a tongue depressor.
Failing this a liner sock is a less than ideal way of solving the problem, but may aid in the reduction of friction, both on your heel and the lining of the boot. Hope this helps! links to the three below!
https://www.cotswoldoutdoor.com/index.cfm/product/anatom-volume-reducer/fus...
http://www.outside.co.uk/shop/Tongue+Depressor
http://www.cotswoldoutdoor.com/anatom-heel-lifts-3E310009?utm_source=catalo...