Normal adult pillows are no good for back sleeping but I found having no pillow wasn't very comfortable. I ended up using a memory foam pillow for toddlers[1] that we originally bought for our son. It's perfect - provides just the right amount of lift for me.

[1] https://www.amazon.co.uk/dp/B004M3PS4O/ref=cm_sw_r_cp_apa_gl...