I think the concern is usually over hot vapors vs. cool ones, but cool mist vaporizer vs. humidifier is your choice. Find something that will be easy for you to clean. I found that the humidifier got too much water on the dresser so I had to put it in a plant drip-pan.
Do not put Vicks in the water or on your child yet. He is too young and children can react to it and develop worse breathing problems. There is a Vicks BabyRub, which is just a soothing blend of herbs with none of the Menthol, so it is safe for babies (I actually use it on myself, too). I also agree about the saline/boogie drops. That can help if the congestion is nasal. Unfortunately, we always still had relciner nights with the kids. It doesn't sound like croup, but you could also try the hot, steamy shower. Hang out in the bathroom with the hot shower running for about 20 minutes before bedtime. We just play with toys and books on the floor or "draw" on the mirror. Hope he feels better!