Hi Miserably Melting,
It would really be a matter of preference depending on how much the protector affects the feel of the topper or toppers. With a foam topper I would lean towards using the topper under a protector to help protect it from the moisture and the body oils that we release each night which can affect the useful life of the foam but but you can air out wool toppers in sunlight which can “refresh” the wool and activate it’s natural self cleansing and deodorizing properties (from the lanolin) so it would be much more of a preference choice. Having the protector on top would maximize protection for the wool topper and having it underneath would maximize the feel of the wool topper.
“Comfort” is very subjective and different people will have very different definitions or opinions about what they consider to be “comfortable”. While I can certainly help with “how” to choose … It’s not possible to make specific suggestions or recommendations for either a mattress, manufacturers/retailers, or combinations of materials or components because the first “rule” of mattress shopping is to always remember that you are the only one that can feel what you feel on a mattress or a mattress/topper combination and there are too many unknowns, variables, and personal preferences involved that are unique to each person to use a formula or for anyone to be able to predict or make a specific suggestion or recommendation about which mattress or topper or combination of materials and components would be the best “match” for you in terms of “comfort”, firmness, or PPP or how a mattress will “feel” to you or compare to another mattress based on specs (either yours or a mattress), sleeping positions, health conditions, or “theory at a distance” that can possibly be more reliable than your own careful testing (hopefully using the testing guidelines in step 4 of the tutorial) or your own personal sleeping experience (see mattress firmness/comfort levels in post #2 here).
Thicker wool toppers will tend to feel softer than thinner wool toppers if you put them on a floor but wool toppers aren’t as a soft foam topper and on a mattress (vs a hard floor) a wool topper can tend to firm up very soft foam layers underneath it or soften up firmer foam layers underneath it.
All the layers and components in a mattress or mattress/topper combination (including the cover and quilting) will affect the feel and performance of every other layer above and below it and the mattress “as a whole” to different degrees so what you feel on a mattress is the combined effect of all the layers and the “mattress as a whole” more than the effects of just a single layer or component but in very general terms the properties and firmness of materials and components that are closer to the top surface of a sleeping system will tend to have a bigger effect on the overall “feel” and firmness of a mattress than materials that are deeper in the sleeping system, thicker layers or toppers will contribute more of their feel and firmness to the overall sleeping system than thinner layers, and a thinner layer or topper would “allow” more of the feel and properties of the layer underneath it to “come through” than a thicker layer or topper.
I or some of the more knowledgeable members of the site can help you to narrow down your options, help you focus on better quality/value choices that are available to you either locally or online, help you identify any lower quality materials or weak links in a mattress or topper, act as a fact check, answer many of the specific questions you may have along the way that don’t involve what you will “feel” on a mattress or mattress/topper combination, and help with “how” to choose but only you can decide which specific mattress, manufacturer, or combination of materials, components, or toppers is “best for you” regardless of the name of the manufacturer on the label or whether anyone else (including me) would have the same criteria or circumstances or would make the same choice.
Once you have had the chance to talk with the manufacturers and retailers that you are considering on the phone about the specific toppers they have available I would choose the one that you are most attracted to based on all the parts of your personal value equation that are most important to you (including the price of course and making sure that you are comfortable with the options you have available after a purchase to exchange or return the topper just in case the choice you make doesn’t turn out as well as you hoped for).
Phoenix