L.M.
Hi M.,
We purchased a humidfier for our home from Sears (Kenmore) and it really supplies moisture in the air throughout the house. We usually turn it on in winter because it is so dry in our house (tile floors). It is a little costly but it pays in the long run. We haven't had much sinus infections or allergies since we have had it. So, if you go to Sears ask them to show you some styles and tell them you want a humidifier for the entire home. They will point you to right location.
For the mattress, you can probably go on the web and find some deals or you can always do what we've done if you didn't have the money to purchase a nice firm mattress and that is to put a thin board under the mattress. I think the babyhomestore website has some clearance on mattresses throughout the year. You can google to their website to find out.
L.