Hi coolmonk,
You can add a wool topper to any mattress but it’s a matter of preferences and whether it was “advisable” or not would really depend on the reasons why you wanted a wool topper.
Some of it’s advantages are that it can add ventilation and helps regulate sleeping temperature to a mattress that needs it, it provides some softness under pressure points (depending on the thickness of the wool), can add some water resistance to the mattress and protect the mattress underneath it from stains, and if the wool and any cotton around it is processed without harsh chemicals it’s a very healthy sleeping surface. Some of the disadvantages of a wool topper are that it can affect the feel of the mattress (which can be a positive or negative depending on what it is used on) and thick wool toppers can develop some impressions as the wool naturally compresses by about 30% which some people don’t like (although it is not a sign of poor performance or the wool degrading which it is with polyfoam). Wool can also be naturally “refreshed” by letting it air out in the sun but it’s a little more difficult to clean than a mattress protector or some toppers where a cover can be removed and washed in a machine. There is more information about wool toppers and some good sources in post #3 here.
Phoenix