When I sleep on my side, I bunch edge of memory foam (lightweight) pillow under my neck so force of ear on pillow is minimal.
Also - when really acting up - small amount of terazol cream (yes, it's a 'vaginal' yeast cream -- and I've also used it for yeast in my dog's ear) on a q-tip swabbed around the ear canal.
In 2007, I had ear tubes placed (not related to this). My left ear, which is the one with the soreness problem, became VERY painful and would bleed when I slept on my left side. After deciding drum was infected at the tube, it was removed. Surgeon was surprised at how infected it was -- even needed to patch the drum. I think that's when I decided to try to treat for yeast.