Before I had my daughter we just bought the middle of the road from JC Penny. After reading about SIDS and other things I would go with an extra firm mattress, and I would get an organic, if I can afford it. I thought organic was silly, but after someone pointed out how much time they spend on the mattress, it makes sense you would want them breathing something other then plastic fumes. Although I also read if you let the mattress sit in your garage or out in the open for a few days most of the chemicals air out.
Best of luck and congrats!!
I agree with another posting . . . if you can afford it, go organic. Organic Grace (http://organicgrace.com/ . . . non-toxic baby section) is having a sell right now. We got the "Organic Cotton/Wool Innerspring Crib Mattress" (the cheapest one) and we are very satisfied with it. I feel better knowing that my son does not breed chemicals 14 hours a day!! And my son LOVES his mattress to the point where he does not fall asleep anywhere else (not even in bed with mom and dad: sniff sniff). I think it is a little thicker then most crib mattress and not all crib bed sheets will fit.
I would definitely go organic. I didn't with my first child so now I have to buy an organic mattress for the next. Do it right the first time and have some peace of mind.
I did a lot of research before buying one, and everything I read said the higher the coil count, the better. However, believe it or not, crib mattresses can be EXPENSIVE! I bought one from Target, a 250-coil, and let it set outside for a couple of days to air it out. I use a waterproof mattress pad under the sheet and crib bedding that was washed and aired out before used.
There is a book called Baby Bargains that has thorough reviews on different crib mattresses. I went with a Colgate mattress they recommended back in the 2004 version of the book and it's been great. Something about crib mattresses is that they are hard, but they are supposed to be that way.
I was going to go with orgainc which arevery expensive but based on theresearch discussed here even that won't prevent SIDS. So I went with the most expensive one sold at Target and bought the baby safe cover mentioned in the above link.
I have two siblings that work for Babies R Us, and they always told me to look for a mattress with 180 spring count or higher, you just want a good firm mattress and if you decide to shop by spring count you can look at any store and get one for just about $50-100+ dollars.. good luck in your search!
I was just researching mattresses for our 4 month old daughter and decided on an organic mattress from Naturepedic. They have no harmful chemicals even for fire retardant and seem to be the only mattress that is certified to have absolutely no off-gassing. You've probably already purchased a mattress by now, but I wanted to send you a link to the study done in New Zealand (that another poster mentioned below) about toxins in mattresses possibly leading to SIDS. What I especially wanted to point out was that the study used a fairly simple solution of "wrapping mattresses in a gas-impermeable cover made from high-grade polyethylene". From my understanding of the study it didn't seem to matter what type of mattress the family had as long as it was wrapped in this polyethylene cover. During the 11 years of this wrapping of mattresses the article states "During this time, there has not been a single SIDS death reported among the over 100,000 New Zealand babies who have slept on mattresses wrapped in a specially formulated polyethylene cover". I thought this was pretty incredible and thought the info might be of use to you in case you didn't go the organic route.
All my best to you and your little one.
Wanted to add some links:
go organic! babies sleep so much and they are breathing air right out of that mattress.
We use the Sealy Baby Posturepedic. They say the firmer the better (if you think it's firm it's probably too soft, so I was told, so go HARD!) and we did some research before buying it. My son has just turned 1 year old, so there may be something out there that is recommended more, but we've had absolutely no trouble with it at all! Good luck!