J.P.
Poor baby. Can you try breastfeeding him in a raised position? It might be easier for him if his head is not in a laying position. Or maybe pump some breast milk and give a bottle or sippy. I don't think I would do a rinse on a small child, I won't do it with my 5 yo because I worry she will breath it in and choke on it.
Hold off on the saline spray and humidifier for a bit and see if some of it dries out.