A hybrid mattress blends foam and pocket springs in one mattress. Usually this involves a more substantial foam layer than other mattresses that are marketed as innerspring.
A hybrid mattress offers a 'best of both worlds' type feel, where there is added support from the pocket coils and a comfortable, pressure point relieving surface.
Though there are latex and memory foam hybrids, the feel of them can be quite different because of the response of the latex vs the memory foam's slow response.
Pros: Best of both worlds with memory foam / latex and pocket coils provide ultimate comfort and support.
Cons: Beware of the foams being used as some hybrids still off-gas or sag because of lower quality materials.
Wool is made of sheep fur. It is sheared from the sheep multiple times in their lives.
The most famous kind of wool being used in mattresses is New Zealand wool because of its attention to quality.
Wool is commonly found in the cover or as a comfort layer. As a comfort layer, it is packed tightly in the mattress so it can add softness to the top layers of the mattress. Some untreated wool may have a slight natural barnyard smell. It is also a natural fire retardent.
Pros: Wool is an all natural alternative to other types of comfort layers.
Cons: The quality of wool bedding is entirely dependent on mattress craftmanship. If the packing is too loose, there can be quick sagging and durability issues.