If you use essential oils, you probably know what works best as a decongestant for you. The original post calls for eucalyptus, lavender, and rosemary. I already had the Breezey blend by Butterfly Essentials and the Breathe blend by doTERRA, so the first two times I tried those blends. Neither one worked great for me, but they hadn't been working great when I put them on my chest either. After battling a cold for a week and experimenting with different oils, I figured out that a strong blend of eucalyptus and peppermint works best for me, so that's what I used in the rest of my shower soothers. My shower is also big and pretty open, so I had to use a lot of essential oil in each disk, like 15-20 drops. I bet that you wouldn't need as much oil for use in a regular sized shower.
adapted from Frugal by Choice, Cheap by Necessity
1 c. baking soda
1/3 c. water
essential oil (I suggest a blend eucalyptus, peppermint, and lavender, or a respiratory blend of your choice)
Preheat oven to 350°. In mixing bowl, mix baking soda and water, adding more water 1 Tbs. at a time, until a putty-like consistency is reached. Line muffin tin with paper liners. You'll only need 5-6. Spoon mixture into liners. Bake for 20 minutes. Cool. Add 10-20 drops essential oils to each cooled disk.