Hi mjosta:
My reasoning for not recommending memory foam as an application for young children was listed in my previous reply. Here is a direct link to that post. “Gel foam” is usually just a marketing term for a polyfoam or memory foam using gel additives.
As I mentioned in my first reply, the brands carried at Sleepy’s (and many of the major chains) don’t meet the durability guidelines recommended. The major brands such as Sealy/Stearns & Foster, Simmons, and Serta all tend to use lower quality and less durable materials in their mattresses than most of their smaller competitors that will tend to soften or break down prematurely relative to the price you pay which is why I would generally suggest avoiding all of them completely (along with the major retailers that focus on them as well) regardless of how they may feel in a showroom along with any mattress where you aren’t able to find out the type and quality/durability of the materials inside it (see the guidelines here along with post #3 here and post #12 here and post #404 here).
Since you said you are limited to choices at that particular store because of your circumstance, I would again refer you back to the mattress shopping tutorial and go through the steps to find the most durable product you can in terms of componentry, keeping within the guidelines I linked to previously about appropriate comfort ranges for children.
As far as the Serta page you linked to, this isn’t greenwashing, but a statement about the materials used. They don’t relate specifics to each mattress, but many of the things thy mention are the exact same things done by other mattress companies, and much of what they relate doesn’t have an impact upon quality or durability. The statement about not using PBDEs, etc., is a reference to their announcement that their polyfoams is CertiPUR-US certified, as is the polyfoam used by most brands. The rest is more about their policies for facility management and recycling- again, none of which relates/describes the quality of the componentry.
Phoenix