latex vs soy foam mattress?

Anyone have any resources they could point me to on benefits of either one or why one would be preferrable to the other? We have two good options for a mattress set for DS - one is a latex foam and the other is soy foam (more like a memory foam than the latex). Both are "green certified" but are not organic so its really just what the manufacturer deems green but we've looked into that bit and are comfortable with it. The salesman I was talking to said in his opinion the off-gassing is about the same in each, better than a traditional mattress but not perfect (if there is such a thing in mattresses without spending thousands) and that they're similarly natural (it was natural latex, not sure if there is any other kind not having much knowledge about latex really).

 Anyway, any thoughts or opinions would be much appreciated. I'm a bit confused as to what to do. I like the soy better but its a bit more expensive (only $80 above the budget we set but still) but if the latex is just as good I would go for that and save the money.... The only real plus to the soy seems to be that because of the memory foam-ness it would hug the body more and be a tad more supportive for DS while he is growing but not enough that the salesman said it was really something to consider.