Hi DesertDuck,
The density of memory foam isn’t directly connected to firmness (see post #9 here) and I don’t have any personal experience with the topper so I don’t know how soft it is relative to other types of memory foam. They would be more familiar with their own toppers than I am so they would be a much better source of guidance about how the firmness may compare to other types of memory foam (at least that they are familiar with) but I would tend to avoid 3 lb memory foam because of potential durability issues and look for 4 lb density or higher instead anyway.
Phoenix