I think my 4 month old has a cold, what should I use?

We are all sick in my house (welcome to Winter in Michigan!) and now I think my 4 month old has a cold too. He sounds really congested, is sneezing, coughing, and has a really bad runny nose with lots of boogers. No fever though (thank god!). What should I do for him? He is also teething. The air in our house is really dry and I tried to use an old humidifier that my mom gave me for a night but 1. I had it on the floor and it soaked my carpet and 2. it's really old and I don't know whether to use warm or cold water (and it doesn't say).