Hi sheep123,
The tightness of the quilting (as you mentioned) along with the type of polyester fiber in the pad and the density of the fill along with the type of fabric used in the cover will all have an effect on the firmness and feel of a fiber mattress pad.
A jersey knit fabric will have more stretch and tend to feel softer than a woven fabric.
There are different species of wool that have finer or courser fibers that are either more or less resilient (merino is a finer species) which can have an effect on how the wool feels and packs down and compresses over time and a mattress pad can also have different densities of wool batting and different quilting or tufting patterns which can also have an effect on its feel and firmness but in very general terms wool will usually compress by about 30% of its thickness over time and will become firmer as it compresses but it will maintain some resiliency even when it is fully compressed because of the curl in the wool fibers. Over the course of the first few months the parts that are under where you sleep most frequently or under the heavier parts of your body will compress faster than the parts where you don’t sleep or that are under the lighter parts of your body but this will even out over time if you rotate it and sleep on different parts of the mattress pad. You can see some additional comments about wool toppers in posts #3 and #6 here.
Wool is a very durable fiber that can last for many years without breaking down so it would be reasonable to expect it to last for at least 5 years for most people before they decide to replace it either because it’s uncomfortable or for hygienic reasons but depending on the person and on the specifics of the wool mattress pad or topper it can last much longer than that and some people will continue to use it and be quite happy with how their wool mattress pad or topper feels for 10 or even 15 years.
Phoenix