Hi sam in seattle,
Both the thickness and the softness of foam layers and the mattress itself will affect the overall softness that you feel. Thinner materials will compress more quickly to a greater percentage of their thickness and get firmer faster so even when they are soft … if they are also thin then they will feel firmer than a thicker layer of the same material. They also allow more of the feeling of the layers below them to 'come through" including if this layer below is the floor or a solid base. Thickness and softness always work hand in hand.
Separate layers will also act a little softer than a single layer of the same thickness.
Option 1: This would be firm enough that it could provide good support for a mattress that had a single 6" core but I agree that it wouldn’t be as soft as your other options and it probably wouldn’t have the “cush” you were looking for.
OPTION 2: This has the same 3" 19 ILD Talalay layer as the next option but the Dunlop underneath it would be softer than the floor (or base) which would be under option 3 and the latex layers are also thicker so this would be both softer than option 1 (softer foam) and option 3. It also has the advantage of using Dunlop in the lower part which can be both soft and also more supportive. This seems to be a good option. It also has more flexibility because swhould the need be there down the road you could change the firmness of half the mattress rather than all of it.
OPTION 3: The advantage of this is that you have tested it but because it only has 3" of latex … the odds are good that it won’t be as soft as Option 2 even though the wool would add some local pressure relief in addition to the latex. It is also lower “value” (price vs cost of material) than either option 1 or 2 which both include more latex although this is partly offset because is has more wool which is also a more costly material.
OPTION 4: This could also be a good choice but much more uncertain and it wouldn’t have the advantage of multiple firmness layers or the flexibility of option 2. Of course you could choose whatever ILD you wished so it could be as soft as you wanted (within the ILD’s that LI offers) but the difference is that it would all be one ILD. If you chose a firmer core it would be more similar to option 1 (a single ILD medium core) and may not be as soft as you wanted and if you chose a softer core then it would be similar to your original idea of two 19 ILD toppers which would run the risk of poor support and alignment.
Overall … it seems to me that option 2 has the better value, flexibility, and both the upper softness that you are looking for along with better lower support (without being the floor) because of the Dunlop below it.
This is strictly a matter of personal preference and which of the tradeoffs between different types of protectors that someone prefers (temperature regulation, affect on the mattress, and degree of waterproofing). This would be waterproof (if that was a necessity), thinner (may have have less effect on the mattress), and warmer and less breathable than the other two main choices. Of course protectors of this type can also be less expensive than either a thin wool protector or a stretch knit cotton protector so this may be a consideration as well.
I haven’t researched all the different types of these protectors for “value” (there’s just too many and my focus is on mattresses more than bedding) but the protect-a-bed elite would be one of the better choices in this group IMO (fabric with a thin waterproof membrane style) because it uses cotton on both sides of the membrane and would be more durable and protect the membrane better.
I haven’t tried the dreamfit sheets so I can’t speak from personal experience (and again bedding is not something that I spend a lot of time researching except as a side effect of my research into mattress materials) but the dreamfit sheets have good reports and seem to work well and be high quality. You would want a fitted sheet with a shallower pocket to keep it snug and secure to your thinner mattress.
Post #7 here and post #26 here include some links to good information and resources for quality sheets although I don’t know how each would “rate” in terms of staying secure on your mattress. In many cases … sheets that don’t stay secure are because the pocket isn’t deep enough for the mattress and this is not likely to be an issue for you 
Hope this helps
Phoenix