Hi samssf,
Mattresses have to be tested for fire retardancy as a unit with the ticking/quilting to pass the fire code (1633) rather than as component parts. Without passing the code by burning an actual prototype … the mattress is not legal to sell without a doctors prescription. Compressed wool can be a natural and effective way to pass the code without the use of chemicals or “socks” or “inherent fibers” and is the preferred choice of many people because of this. It is the most natural method of passing the fire code.
The organic ticking/quilting uses wool as the fire retardant and this is what would have been included in the prototype they passed. Without the wool or with a different ticking (like the diamond) … the mattress probably doesn’t pass (quilted latex is much more difficult to pass the burn test) and a different type of fire retardant would have to be used for the mattress to be legally sold without a prescription.
A good quality ticking is one of the most expensive components of a mattress and can be a significant part of the cost of a good quality mattress. This is especially true with more expensive fibers like organic wool and cotton (and others). The more wool that is in it and the higher quality fabrics that are used, the more expensive it will be. A good mattress ticking is an essential part of a mattress though especially with latex which can degrade with exposure to ozone and ultraviolet light and a mattress protector or pad is not enough to protect the latex.
Foam Order’s wool layer is thicker than normal which results in a more expensive ticking. (You can see some high quality but lower cost options here and here). If you go here you will see on their site that the 9" organic mattress includes the organic cover and if you go through the process it’s a little less than if you just choose the components. I find their site a little bit confusing sometimes and I have mentioned this to them.
While Form Order has good quality and better value when compared to more typical choices … they are not in the same value range as some other factory direct manufacturers including some of the online manufacturers that are members of the site who can include either Talalay or Dunlop latex in similar layering with a quilted wool cover for a lower cost. Just in case you haven’t seen this … there is a list of some of the better San Francisco outlets in post #2 here.
Sleepworks is a good choice and if you can take the drive I would also highly recommend you include Bay Bed in your research. They are a member of the site and have great quality and value. They specialize in pocket springs with latex and are also a “component” mattress with a zip cover.
Innersprings, polyfoam, Dunlop latex, or Talalay latex in a support core all have different feels and types of response. Besides the amazing durability of latex support cores … it has many other advantages including the choices of firmness available (can be better customized), the ability to adapt to different needs and sleeping positions and weights, it’s motion separation, it’s progressive firmness, and its point elasticity. Of course it is also the most expensive of the mattress cores so for those who want the “feel” of latex in the comfort layers but prefer a lower cost support system, then an innerspring or polyfoam (good quality) with latex in the comfort layers can also be good choices for lower budgets. There are also some who simply prefer the feel and response or “bounciness” of an innerspring and for these it would be a matter of preference.
Latex (especially natural latex) is a natural repellant to dust mites and would be more effective than an innerspring. The lanolin in natural wool is also repellant to dust mites. There are some good dust mite suggestions here (and many other places online although there is conflicting information as well). Of course if dust mite allergies are a real issue then a mattress protector that encases the mattress and has a tight enough weave to keep them from passing through can be an important part of managing allergies.
A latex mattress is heavy and needs a firm unyielding and strong slatted support base (or a tension adjustable slatted base for those who wish to fine tune their mattress this way). If you are putting slats on your bedframe, then it’s fine to put the mattress on top of these but they should be very strong, supported in the middle if your mattress is larger than a single, and no more than 3" apart and preferably less (“closer to 2”).
Hope this helps and answers all your questions … so far 
Phoenix