Hi 8grands,
There are too many unknowns and variables involved to make specific topper suggestions because softness and firmness can be subjective and relative to different body types, sleeping positions, and individual perceptions as well as the softness of the mattress which will also affect how soft or firm your mattress/topper combination feels but post #2 here and the topper guidelines it links to has more information that will help you use your sleeping experience as a reference point and guideline to choose the type, thickness, and firmness for a topper that has the best chance of success.
Most latex will have some initial odor which can vary based on the type and blend of the latex and on the sensitivity of the person to specific smells (some people are more sensitive to certain smells so it can smell smell stronger to some people than others) but for most people it will dissipate to levels that they don’t notice in a few weeks (see post #2 here). All the latex that you will encounter has been tested for harmful substances and VOC’s either by Oeko-Tex or Eco-Institut so any smell isn’t harmful (see post #2 here).
Phoenix