Not sure if you found someone already. I was given this name and number from a friend who had her mattresses cleaned. I haven't tried the service yet myself, as I have too many other things going on. Here is her number -Karol at 6031-1312.
If they have allergies, you may want to consider an organic natural rubber mattress. I've just ordered one from the US at www.gobabygogreen.com. Tried to get a cot sized one here in HK but couldn't find one anywhere.