Hi kat888,
This will also vary depending on the specifics of the wool topper, your weight range and body type and sleeping positions and your individual perceptions but it will likely have both a softening and a firming effect at the same time that would combine together. The surface “feel” and firmness would probably be a little softer than a medium latex topper but the wool topper would also reduce the ability of the latex underneath it to contour to the shape of your body so it would likely firm up the latex as well. You will feel the effects of both toppers at the same time (along with any influence that comes from your mattress as well) and which one would be “dominant” would depend on the person because there are different types of firmness/softness that different people are more or less sensitive to that can affect how they rate a combination of materials “overall” (see post #15 here).
In very general terms wool toppers that are thicker or that contain more wool would generally feel softer but the breed used for the raw wool and the thickness and resilience of the wool fibers, the compression of the wool batts, the tufting or quilting of the topper, and the overall processing, construction and layering of the topper along with the amount of wool inside will all affect the feel and performance and the firmness of the wool topper so I would suggest a conversation with any retailer or manufacturer you are considering to talk about a specific topper and your experience on your mattress if you aren’t familiar with a specific wool topper or with wool toppers as a whole.
Phoenix