Hi HermitageBrewing,
Ditto to what dn said 
A cotton topper will generally feel firmer than wool … especially when it compresses over time … but this will also depend on the specifics of each topper and the layers underneath it.
The only way to learn how different combinations will feel and perform for you is with extensive testing on different combinations or your own personal experience when you sleep on the mattress so you can translate “theory” into your own personal experience.
The first part of post #2 here also has some ideas (including split layering that dn mentioned) that can be useful for couples whose needs and preferences are different.
Phoenix