I will share what I have learned since beginning my own search for a chemical free mattress for my child. The first thing I looked at was, of course, the Organic Cotton and Wool by Vivetique. I did not know what else was out there. It seemed the most affordable. Then I found out it was really recomended to use with a boxspring, as that is what the mattress was designed for. That brought the price up. I looked at The Rose mattress, the most budget priced, but it had the same boxspring hitch, and seemed like a very firm mattress. In fact, since selling these for several years now, I have realized these two models are in fact the very firmest models we sell. If you are looking for very firm in a conventional style, then those models are a good bet. If you do not want to use a boxspring, the Apollo, which can be used with a wood foundation, or directly on a slat frame is a great choice. It also ships quicker than a Vivetique mattress. I began to look into the Paradise, which has 2" soft latex on top of the innersprings. I felt like this would add more comfort, as latex does not compress the same way that cotton and wool do. Because of the latex, you can use it without a boxspring and it is also more mold and mildew resistant, as well as dustmite resistant. All those just seemed like good features to me, especially in a child's mattress. Since beginning this business I created the Budget 4" Latex mattress, which has no innersprings. It does not need a boxspring - can go directly on a slat frame - and is a very comfortable mattress which will last a long time. Another bonus to the Budget Latex options are that the twin size can be rolled up and shrinkwrapped and shipped UPS as opposed to freight company, which saves lot's of money. (sometimes hundreds!)
So my favorite picks for children are either The Paradise, or a solid latex mattress. If money is not an issue, the Natural Latex by Vivetique, or it's PureRest brand equivelant, The Harmony are wonderful choices. If money is an issue, check out the 4" Latex. If funds are super tight, I would get a Super Budget 2" latex any day over any conventional mattress out there. Even the 2" is still a very comfy bed. If you begin with a budget base when your child is young because budget is a concern, you always have the option to add a topper later, if more comfort is needed.