I have just read your post an I am sorry to hear about your son. I did put up a way of using Soya milk by adding it to either a smoothie for breakfast or as a milkshake with plenty of fresh fruit to hide the taste.
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As I am a nanny out here in Hong Kong I know a lot about asthma, excema as many children out here have it due to the high pollution rate that we have.
The youngest girl I look after has excema and after trying the western medicine way, we went to see a homeopathic dr who gave us a cream and drops and even though my boss laughed at the idea it has all gone and we just use the cream now after swimming.

These are a few tips in general that I have picked up. These help to reduce toxins and pollutants in our home.

Don't bring your shoes into the house, this is apparently the biggest transporter of lead in to your home. This is mainly from the lead laden tarmac you walk on.

An air purifier or humidifier or ioniser will help to filter the impurities in the air we breathe, but even opening a window at night when you go to bed will stop you breathing in stagnant polluted air for 8 hrs. obviously if you live on a busy road this would not work due to traffic pollution.

Be aware of the detergents you use. Try to use biodegradable as your body can process and eliminate the toxins. This is very important in clothes and bedding as we spend up to 8 hrs in bed or even better environmentally friendly products as these don't have bleaching agents in them which has been related to Asthma.

I hope this helps a little bit.