TB -
It looks like you've received some great advice already. Just a couple additional thoughts:
Look out for adults spreading germs. People are contagious for a day or so before they show symptoms of an illness. Our son was a preemie, so we had to be unusually careful, but we had every adult who entered the house scrub his/her hands such that he/she was ready to perform surgery. My husband and I also made sure it was the first thing we did upon returning home. Our doc made a big deal about the grocery store. Imagine someone sneezing in his hands, pulling something off the shield, deciding he doesn't want it, putting it back on the shelf, and then you, unknowingly, pick up the item. Blech! I agree that you need to let your kid get sick, but, for his first winter, I would personally keep him a bit more protected. You're smart to stay away from chemicals, but you might want to use a liner for where he sits in the grocery cart for this one year (could likely find a used one), and, better yet, if you have the ability to go grocery shopping without him, do so. Don't let adults touch his hands unless you know they've done a proper scrub (for two "happy birthday" songs). They can touch his leg or arm or back, but not his hands or near his mouth/nose. Again, we were under doc's orders on this, but I remember being shocked at how many adults reached right for our baby son's hands without even washing their own first. We explained we were under doc's orders to be quite vigilant his first winter, and if someone got bent out of shape, that was his/her problem. Most people were very cool about it, though. So, careful of all aspects of the grocery store, be sure that everyone entering your house (including you if you don't do this already) goes straight to the sink. No need to get germs on drawer pulls and door knobs. You can often use your forearm to turn the kitchen sink on before you scrub. Does this sound insane? Perhaps. But, given that your son is getting so many colds, you might be able to eliminate a few this way and still let him play with other kids (who, admittedly, are little petri dished) on occasion. You can also wipe down communal toys/equipment when he's around other kids. Given the difficulties inherent in washing a 9mo old's hands, it's easier to keep people and items touching him clean. Good luck!