Hi LookingNow,
Wool can certainly be used as the fire barrier in a mattress (see post #2 here and the videos that are linked inside it) and there are many manufacturers that use it instead of other types of fire barriers (some of which such as the inherent viscose/silica fire barriers also don’t use any chemicals). You don’t need a prescription to buy a mattress that uses a wool fire barrier to pass the testing regulations … only to buy a mattress that hasn’t passed the fire regulations. There is more about fire retardants in post #2 here and in post #4 here.
The innersprings in a mattress aren’t normally the weak link in a mattress in terms of durability and it’s almost always the quality of the foam above the innerspring that will be the first to soften and break down. There is more about the factors that can affect durability and the useful life of a mattress relative to each person in post #4 here. There is also more about the different types of innersprings in this article and in post #10 here. A good Bonnell coil with a good insulator and good quality foam on top (such as latex) can be a very durable choice.
If the Bonnell coil and an insulator and the latex are the only layers and components in the mattress then there would certainly be no weak links in the mattress in terms of durability and the price is reasonable IMO.
I can’t answer whether it would be worth it for you to have a few more finalists in the mix when you are making your final choice (I would personally prefer to choose between two or three finalists) but a visit to Spindle will certainly let you compare an all latex mattress to an innerspring hybrid to see which one you prefer in terms of PPP. There is more in post #2 here about innerspring support cores vs a latex support core.
Phoenix