We've tried heating the room for my dd when she has the same kind of cough, Vicks vapor rub on the feet with a pair of socks over the top, I've found phenergan works better than cough medicine - sometimes its more of an allergy cough than a sickness cough, and the sedative side helps her get a better sleep.
A spoon full of honey sometimes helps coat the throat a little to keep it from drying out too