Hi yianni54,
You have certainly eliminated all the “worst” options and narrowed things down to some good choices which is great to see 
While I can’t speak to which may be “better” for you because that has many different parts and is based on each person’s “value equation” … I can certainly make a few comments of things that I would be looking at in making a decision between them.
I think that this probably has to do with the specific layering of each and the ILD’s in each mattress much more than the differences in materials. While there is a difference in Dunlop (used in the Core layer of BE) vs Talalay that most people can feel … the difference between 100% natural Talalay and blended Talalay is much less obvious and many people can’t tell the difference at all. Of course the difference would be more noticeable in a mattress that was all one type of material than it would be in just a single layer.
In and of itself no. For someone that slept on a mattress which had a single 6" core layer that was perfect for them there would be no benefit in having two 3" layers of the same ILD. On the other hand … two separate layers that can be layered with different ILD’s can provide design flexibility that isn’t possible with a single 6" layer. In some cases this can be a benefit in terms of fine tuning a mattress for someone’s unique needs and preferences and there are also cases where this can introduce a level of complexity that can be confusing. In other words … it depends on the person and the goal of the design. Each has its pros and cons but one is not intrinsically “better” than the other.
They are owned by Latex International whch is one of the two main Talalay latex manufacturers in the world and the largest supplier of Talalay latex to mattress manufacturers in North America. They are very responsive to retailers (which are their customers because they don’t sell directly to consumers) but also to consumers as well.
They are very different because they have an organic cover quilted with organic wool which is very high quality and much more costly than either of the other unquilted covers you are mentioning. While some people prefer a thinner stretch knit cover (such as the one used in the PLB which is also high quality but not nearly as costly) others prefer wool in the quilting because it is used as a fire barrier (so they don’t need another type of fire barrier) and wool can regulate temperature very effectively. So this may also not be a “better worse” comparison but in cost and quality terms the FSF is certainly higher quality and a more significant part of the overall cost of the mattress. The BE also has a high quality wool quilted cover.
I understand this and it’s a common “feeling” when someone is considering an online purchase and is also part of what each person needs to take into account in their personal value equation.
Some suggestions about some of the differences between your choices that may be important to you or at least worth considering …
From a commodity point of view in terms of “value” … FSF uses a more costly version of latex in their mattresses (100% natural is more expensive than either Dunlop or blended Talalay and in the same range as Dunlop that is certified organic) and is the better “commodity value” of the three based on the relative cost of the materials and components in the mattress.
Both the FSF and the BE can be adjusted after the fact (to different degrees) if your choice needs some fine tuning while the only option with PLB to do this would be adding a topper or exchanging the mattress. FSF is the most customizable of all of them because you can re-arrange the layers if you need to and you can also do a layer exchange for one of your layers at the cost of one way shipping should you need this.
Both FSF and BE have the ability to replace a comfort layer down the road should this be necessary for durability reasons or changing comfort needs. With FSF you can replace any of the layers. PLB doesn’t have this ability.
Of course PPP (Pressure relief, Posture and alignment, and Personal preferences) is a significant part of the “value” of a mattress and only you can decide which you believe will best match your individual needs and preferences. I would make certain that in the testing you have done you have tested specifically for pressure relief and support/alignment on each mattress rather than just going by the more subjective standard of 'comfort". Because you haven’t tested the FSF … this would be “theoretical” based on your knowledge of similar materials, your conversations with the manufacturer, and on the ability to re-arrange or exchange layers. I normally use a 20% “premium” with an online manufacturer vs a local purchase as being roughly equivalent value but each person knows their own risk tolerance better than I do and may assign a different number to any added risk that they perceive.
I’m not sure if all of these include a foundation or if they are “mattress only” or for a set. If you are comparing prices for anything other than mattress only to mattress only then the comparison wouldn’t be comparing apples to apples. Anything that is added to the mattress purchase is part of its “value” including other services offered by each merchant and these would need to be compared separately from the mattresses themselves. I always prefer to compare each component separately (meaning mattress only to mattress only comparisons and then similar comparisons to any other extras that are included). This is a much more “accurate” way to compare the value of each mattresses.
I would also take into account that the Worlds Best Bed is the softest mattress they have and for many people it may be too soft for the best alignment once they sleep on it on a regular basis. For others it may be fine. Either way … I would make sure I had specifically tested it for alignment and not just evaluated it’s “comfort” which is a much more subjective and less accurate way to buy a mattress.
So hopefully this will give you some ideas about how to choose and compare so that you can better decide what to choose between some good options.
Phoenix