Hi cabert,
While other people’s comments about the knowledge and service of a particular business can certainly be very helpful … I would be very cautious about about using other people’s experiences or reviews on a crib mattress (either positive or negative) or review sites in general as a reliable source of information or guidance about how suitable, how durable, or how “safe” a mattress may be for your child because most people that write reviews have very little knowledge about what they purchased or the materials inside them.
If you have spent time reading the children’s reference post here (which includes several links to topics about crib mattresses) then you would likely know more than the large majority of the people who are writing reviews so using reviews as a guideline would be using the opinions of mostly uninformed consumers to guide your purchase which really wouldn’t make much sense.
When you can’t test a mattress in person (or when it isn’t necessary such as in the case of a crib mattress where you already know that you need a firm mattress) then the most reliable source of guidance is always a more detailed phone conversation with a knowledgeable and experienced retailer or manufacturer that has your best interests at heart and who can help “talk you through” the specifics of their mattresses and the properties and firmness of the materials they are using (fast or slow response, resilience, firmness, temperature regulation etc) and any options they have available that may be the best “match” for your child.
Other than that … there really isn’t too much that I can add to the information in the posts about crib mattresses that are linked in the topic about mattresses and children.
A warranty is just to cover defects and aren’t particularly important in a crib mattress which you won’t be using for a long period of time anyway. In the My Green Mattress a defective coil system is really the only thing that would cause an impression that deep (although any mattress that uses natural fibers will develop some impressions as the fibers settle and compress) but the warranty isn’t something that I would be nearly as concerned about with a crib mattress as the type and quality of the materials inside it.
My Green Mattress/Quality Sleep is one of the members of this site which means that I think very highly of them and I believe that they compete well with the best in the industry in terms of their quality, value, service, knowledge, and transparency and I certainly wouldn’t hesitate to purchase a mattress from them (or any of the other members of this site).
I wouldn’t be concerned about corners that are slightly rounded as long as a mattress fits the crib without “gaps” in the sides, top, and bottom.
Outside of the relative “safety” of the materials in a mattress … the most common allergens would be to dust mites and other particulate allergens and there is more about dust mite allergies in post #2 here and the posts it links to. A good mattress protector or encasement (waterproof in the case of infants and young children) that can be removed and washed would make a bigger difference with dust mite allergies than the materials in a mattress.
The Pebble Lite is polyfoam (which is CertiPUR-Us certified) … not latex.
There is more about latex allergies in post #2 here and I haven’t read any information in many hundreds of hours of reading that would give me any cause for concern for infants or children with the foamed latex that is used in mattresses.
I don’t know their weight limits either but if it meets the current CPSC crib safety standards then it “should” be OK.
IMO … any of the crib mattresses you are considering (whether they are a single firmness or dual firmness) would be suitable in terms of firmness for infants or younger toddlers until they are ready to transition into a larger bed (generally between about 18 months and 3 years).
Phoenix