Hi iheartpandas,
Most of the wool lanolin is removed during cleaning and scouring and there is more about wool allergies in this topic and at the end of post #2 here.
It can vary from person to person and from topper to topper depending on the type of wool used and how it is processed and the construction of the topper but in most cases those who are sensitive to wool or lanolin would be fine with a wool topper because they wouldn’t have any direct contact with the wool itself if it was surrounded by a cotton cover.
If you are uncertain it can also be a good idea to check if the manufacturer or retailer you are dealing with can provide sample that you can either rub or wear against your skin for a day or so to make sure that you would be fine with that specific product.
Phoenix