Hi Jewels,
As you (hopefully) know from the time you’ve spent here … I would tend to avoid buying a Sealy or any major brand (see this article). It’s also very unlikely that they will tell you the specifics of the fire barrier that they use (they are not particularly transparent about any of the materials or components in their mattresses).
I’m not sure which of the Therawrap mattresses you are looking at but it’s possible that it includes some memory foam which tends to sink in more deeply as you sleep on it over the course of the night. I would make sure that you can find out the quality of the materials inside it before purchasing this or any other mattress (see this article).
If you are not confident that your testing will do a good job predicting how well you sleep on a mattress then I would pay particular attention to the options you have available after a purchase to exchange or return the mattress (or in some cases to exchange individual layers of a mattress) so that you can use your actual sleeping experience to decide on whether a mattress is a good match for you. There is more about the most important parts of a successful mattress purchase in post #13 here.
This would depend on what you consider to be “safe” and on how you answer the very complex and controversial question of “how safe is safe enough for me”? (see post #2 here) since all mattress materials could be considered to be “safe” by some standards. For example the CPSC (Consumer Product Safety Commission) considers all mattress materials to be “safe enough” or they can’t be sold to consumers although of course there are many consumers that are more concerned about the materials in a fire barrier than they are or have more specific criteria for “safety” than the CPSC (see post #2 here and post #4 here for more about fire barriers).
Phoenix