Hi Lnr103,
I had some catching up to do in this thread!
They are listed on the CertiPur site here* 
ADMIN NOTE: *Removed 404 link|Archived Footprint: certipur.us/pages/for-consumers/find-products/
As dn mentioned … latex is a very resilient and “springy” material so this would be part of all latex mattresses to different degrees (depending on the type and firmness of the latex and the design of the mattress and the cover/quilting) but outside of the resiliency there is no “standard” feel with a latex mattress because like all mattresses there is a wide range of different designs that use different types of latex and firmness levels that will each have a different “feel”. Your budget would be within the range of some “all latex” mattresses but it would depend on the thickness, the manufacturer, and the specifics of the design and type of latex. It would also be well in the range of latex hybrids that have latex in the comfort layer and then an innerspring or polyfoam support layer.
This would be OK in a two sided mattress but I would be very cautious with 1.5 lb polyfoam in the comfort layers of a one sided mattress in amounts more than “about an inch or so”. 36 would probably be the ILD of a support layer which is not a “quality” spec but a “firmness” spec.
This would depend on how important your sheets are and how well they would fit your new mattress (which I don’t know) but the suitability of a mattress has much less to do with its thickness and much more with what is inside it and the specific design. You could always bring in a set of your sheets and “make the bed” in the showroom to see how they worked (in a mattress store nobody would probably blink an eye :)).
It’s probably blended Taalay but I would always make sure you find out the specifics about any mattress you are considering. You can’t really tell the difference between blended and 100% natural Talalay by appearance and they both “feel” very similar as well (although 100% natural is more costly). The fire barrier is most likely an inherent rayon/silica fire barrier (see post #2 here) which is non chemical and I would consider to be very safe.
Many sites that either sell or are a hidden link to retailers or manufacturers that sell the type of latex they recommend will often “recommend” one type of latex or another … often based only on opinion that is “presented” as being more authoritative than it is. You can read a little more about the different types and blends of latex in post #6 here. There is no answer to “how much” latex you can buy for a specific amount because a mattress is very different from buying latex by the inch and it will also vary greatly between manufacturers. The members here that sell latex mattresses online are listed in post #21 here and there is a wide range of different designs, options, and price ranges there but in addition to being good sources for latex mattresses they can be a very useful “value reference” as well. While latex can be just as pressure relieving as memory foam, it has a more “on the mattress” feel to it while memory foam has a more “in the mattress” feel. Post #2 here has more about the difference between them. There are some types of latex which are “slow response” versions (such as Talalay GL slow response) which have some of the “feel” of memory foam. If there is a Pure Latex Bliss dealer near you (you can just enter your zip here) they may carry some mattresses that use it.
If they carry both Talalay and Dunlop they would be a great place to get a very good sense of different types of latex and layer combinations.
dn’s comments are well worth taking to heart as someone who has both purchased a great mattress and is still “experimenting”
Phoenix