Hi alwaysat,
Yes … this is one of the more common configurations that is available from many online manufacturers or retailers that offer component latex mattress “kits” (see post #3 here) and is a common design for those that are building their own DIY mattress as well…
There is more about the pros and cons of a single 6" core vs two separate 3" layers in post #2 here.
If you are attracted to the idea of designing and building your own DIY mattress out of separate components and a separate cover then the first place I would start is by reading option 3 in post #15 here and the posts it links to (and option #1 and #2 as well) so that you have more realistic expectations and that you are comfortable with the learning curve, uncertainty, trial and error, or in some cases the higher costs that may be involved in the DIY process. While it can certainly be a rewarding project … the best approach to a DIY mattress is a “spirit of adventure” where what you learn and the satisfaction that comes from the process itself is more important than any cost savings you may realize (which may or may not happen).
There is also more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support” and “pressure relief” and “feel” that may be useful as well.
For those who decide to take on the challenge then I would either use the specs (if they are available) of a mattress that you have tested and confirmed is a good match for you in terms of PPP as a reference point or blueprint and try and “match” every layer and component in your reference mattress as closely as possible or use a “bottom up” approach (see post #2 here).
This is something that only you can answer depending on your risk tolerance and any risks involved in your lifestyle. For many people the answer would probably be no since the odds of a fire are relatively low and for some people that are much more risk adverse the answer would probably be yes. Many knit covers that don’t use wool quilting as a fire barrier include an inherent fire barrier instead although they may not have been tested and passed the fire regulations with the specific layer choices you end up choosing.
There is more about the pros and cons of a wool quilted cover vs a thinner and more stretchy knit cover post #6 here.
I’m looking forward to finding out what you end up deciding.
Phoenix