I'm not a pro, so we'll have to let those who are give you install tips. However, I have an older home where some of my floors are extremely unlevel, and was told that either sheet vinyl or W2W are the best options for such floors.

There are some remarkably attractive patterns in sheet vinyl flooring these days, so you might want to consider this. It won't add to the value of your home the way HW does, but it might be less expensive for both materials and installation.

You can level floors with leveling compound, but that's a big job for an entire home and limited DIY skillsets.

the floors have to be level period. You won't be happy and the product won't last if installed incorrectly. You have to get an estimate on cost of floor prep but it will be necessary if you wish to swithc to hardwood.

I too have severe asthma and allergies. One source for good information about anything to do with a house and potential problems is the American Lung Association. (For example, after we remodeled some years ago, I had horrible reactions. After six months of increasingly desperate searching for answers, an ALA booklet for health care professionals finally alerted us to the pilot light of our gas stove, of all things.)

I too have to stay away from all carpeting. We are currently building a house with all floors in tile or wood for that reason. We recently started looking at vinyl for some of the storage areas, and we have found some fantastic products. I would definitely consider them for a remodel. They are far easier to install than wood, not as costly as wood, they are as easy or even easier to maintain and keep dust-free, and they are easier to redo if down the road and with more time to act, you may want to try for wood. I would check with the ALA about off-gassing of different materials, glues, etc. to make sure your son can tolerate the installation process or how long after installation he may be vulnerable.

You have my empathy.

You might be able to find a floor installer who has the knowledge to look at your floor and give you some ideas for a fix.

You first need to find out why the floor is 'unlevel'...is it just the addition that is the problem or does the original section have unlevel areas also?

You need someone to look at them. Either a knowledgeable builder - remodeler or a very good flooring professional. It's no use guessing, you need real information. We do not even know if the floors are wood or concrete.

Hello again, and thank you to everyone who has responded to my post...I do appreciate it!

Well, currently underneath our carpet is a wood subfloor...which is over a basement... which is a finished basement with drywalled ceilings (yes I know that makes things more difficult). By the way our current floor "creaks" in many different places, even with the carpet. At this point I am not ready to give up the idea of hardwood. I am also willing to pay extra money and take any extra precautions for enviro friendly products to ensure the safety for my son. But of course I only want to do this once.

I know I need the advice of a professional, but I guess I just don't know where to turn. I don't know any builders. I have spoken with a couple of flooring installers but I can tell they are not knowledgeable enough to tackle this. I can't believe there aren't contractors that specialize in restoring floors? I would think that many older homes experience this same dilemma. I have joined Angie's list but still have not been able to find contractors that sound like what I am looking for. Ditto for Craigslist. Am I missing something?

A good 12mm laminate floor may be a good alternative for cost and performance. But the subfloor unlevelness still needs to be fixed.

"the floors have to be level period. You won't be happy and the product won't last if installed incorrectly. You have to get an estimate on cost of floor prep but it will be necessary if you wish to swithc to hardwood"

Level and flat are not the same thing.

Floors need to be flat for a decent hardwood install, they do not have to be level.

Even the flatness can be violated if the numbers are small fractions of an inch over many feet.

A real 3/4 inch hardwood floor is actually rather forgiving of minor substrate defects, much more so than the thin 'engineered' floors.

You may have to think hard about floor finishing though.

Site finished floors may cause problems for you son until the finish has cured (usually about 5-7 days).