Best Mattress for Asthma/Allergies

I have a 7 year old girl who has asthma and is allergic to dust mites and tree pollen. Can anyone recommend a mattress that works really well for allergy and asthma sufferers?

She has wood floors in her room and currently a HEPA air cleaner. She also has an allergy mattress cover. I need to get her a new mattress and have been looking at latex. Any suggestions on a specific mattress that has worked well? She does not like "hard" beds and I've read that latex tends to be on the firm side. Thanks!

Recently I bought a new mattress because I have asthma and dust mite allergy also. When I got it home and opened it it had an overwhelming latex smell to it. The whole room smelled like latex, and it irritated my lungs. So I had a difficult time breathing and sleeping on it the first night. I opened the windows and let the room air out the next day and put an allergy cover over the mattress and box springs and it got better. Pillow covers work well too for dust mites too, so they're not in your face. I have read that latex bothers some people with asthma. Just wanted to let you know since your mattress shopping. My allergies and asthma got much better after I got rid of old mattress and pillows. Hope this helps. Good luck!

PLEASE try using silk and cotton blend sheets. I have severe dust mite allergy. When they tested me, the band of hives ran clear around my upper arm. For many years, I woke every day to massive hives the size of softballs that even after they cleared, left hemorrhage marks in my skin for days. The itching was nearly unbearable. I was given atarax and zyrtec, and at one point, zyrtec twice a day. Then I found out about silk.

http://www.youtube.com/watch?v=-LIlgO4pFtY

If you don't want to watch the whole video (it's FASCINATING!) just go to about the 5:20 mark for the information about dust mites. I have since bought silk clothing, a 100% silk comforter, and silk/cotton blend sheets and pillow cases. I NEVER wake up with rash! It's heavenly! I now only take a single zyrtec daily to help control my allergies.
Overstock carries the silk/cotton blend sheets so reasonably, it is just not worth not trying. Originally, I paid MUCH more from other suppliers to buy the first silk bedding. You can buy the 100% silk comforters from "Moon's" on ebay. I HIGHLY recommend him as a source to obtain the quilts! Sister's Silk on ebay is also a fantastic supplier of beautiful silk clothing. I recommend that you try silk. It may or may not help you, but before you spend a fortune on silk, try utilizing some of the "alternative" sources, like ebay.
I have spoken to numerous allergists about silk, and unfortunately, not a single one of them knew that dust mites would not get near silk. I am so thrilled to find this forum to let others know. There are even silk crib sets for babies. I HOPE that as people become aware of the natural remedy of silk for some of these allergies, fewer and fewer will find it necessary to use nebulizers.
You can use ANY mattress if you use silk. The dust mites will NOT get near your bed. If they are not near your bed, you are NOT breathing in their "dust" while sleeping. Hope this helps all of you.

if you do get a temper-pedic make sure to let it air out, they have a smell to them and need airing out.