Hi madinsomniax,
It sounds to me like your mattress is a good candidate for a topper … firm and less low density polyfoam in the comfort layers.
the choice between Dunlop and Talalay is a personal preference (like asking what should I eat today) but Talalay is typically available in softer versions that Dunlop toppers and I think that most people of your weight would probably prefer it.
Everyone has their own “definition” of what they consider to be soft and firm and different body types, sleeping styles, and perceptions can make a big difference in what someone “feels” as being soft or firm but for most people talalay in the 19 - 24 range would be considered soft and in the 28 - 32 range would be considered medium to medium firm.
They have a different “feel” and Dunlop isn’t as consistent across the surface as Talalay (it has a wider range of ILD’s in the layer because ILD’s are never exact) and has a higher support factor (gets firmer faster than Talalay as it compresses) which is just as important a part of how soft a layer feels as its ILD. I think it would be fair to say that for most people Dunlop in a particular ILD will feel firmer than Talalay and closer to the next step up in ILD. This is very approximate though because softness and firmness is very subjective.
I think you will find that it will vary even with the same manufacturer and Dunlop will usually smell like Dunlop and Talalay like Talalay but I don’t know of one that would consistently be much different from another (there may be but I don’t know of it).
A good manufacturer or retailer will have a good quality cover either that comes with it or that they recommend. Two of the most common are a stretch knit cotton or bamboo. It just needs to be thick enough (not for example like a mattress protector or a sheet over the latex) to protect it from air and light which will degrade latex faster.
The better options I know of in the Asheville area are in post #4 here but I don’t know which may carry toppers so I would call them before paying any of them a visit.
Post #2 here and the topper guidelines and online sources it links to may also be helpful.
Phoenix