Hi rosscohen,
I don’t know the specifics of the fire barriers in each mattress but there is more information in post #4 here and post #2 here about the different types of fire barriers and which ones may be more “safe” than others and don’t involve harmful chemicals. You would need to ask each retailer or manufacturer what type of fire barrier their mattresses contain or in some cases if you have a prescription from a medical professional some manufacturers will make a mattress without a fire barrier at all.
Many latex mattresses use quilted wool as a fire barrier which is perhaps the most natural and for most people the “safest” or often the most desirable of all although inherent viscose / silica fire barriers are also very safe IMO and are often used in mattresses that don’t use quilting for those who want to sleep closer to the latex.
Phoenix