My DD has a cold and is very blocked up. And like adults it's worse when she's on her back.
I have raised the head end of her cot, use saline drops throughout the day, rub a little Snuffle Babe in her chest and back and if she's particularly bad would give her Calpol.
But she wakes so many times through the night and am sure its due to her being uncomfortable sleeping on her back.
Anything else maybe I'm missing?