I slept with a pillow under my bump, one between my legs (not too high though) and one behind my back for support. I switched sides when I felt uncomfy but it was a bit of an ordeal moving my 'nest'

I also had a thin summer doona doubled up under the fitted sheet on my side of the bed. We have a pillow top mattress but it didn't help with the pain. The doona did help a bit though. The suggestion of some cheap foam is an excellent idea.

I also used a heat pack and panadol. It was tough going but most of the pain went as soon as labour started and the rest not long after so keep that in mind when you're feeling down.

Good luck. It is awfully hard to get comfy and decent sleep in the last trimester