Warming that cold spot on your back .

Winter is here and I am still riding , found that when we are 2 up somehow the chill gets in between the two of us and my lower back gets damm cold . Mr chill somehow gets under my jacket and My partner say here lady part freeze  :imaposer: , We have tried a small hot water bottle , but it seems to get cold fast , Maybe a fleece scarf folded up behind my back , closing /filling the gap so no wing can creep up from under ones legs could help . Will try out some ideas on our ride this weekend .