Hi whift47,
I haven’t use the combination personally but I know many people have (and organic mattress manufacturers that suggest it) and it works well … except I would use the wool puddle pad under the cotton encasement rather than over it. The cotton can help wick and spread out the moisture into the puddle pad to improve its water resistance and it will also feel better to most people. I don’t know of any “all in one” combinations.
There is a little more about mattress allergy encasements and what to look for in post #2 here.
I haven’t done much research into wool puddlepads and bedding isn’t an area of specialty for me but some google searches on “wool moisture pad” and “wool puddle pad” will bring up many options. In general they will either be felted, needlepunched, or tight weaves to help densify the wool and help with water resistance. There are also differences between them in the amount of wool content and the thickness of the puddle pad and in my experience it can be a good idea to talk with a knowledgeable retailer or manufacturer about how their product compares to others in terms of the type of wool they use, the method of construction, the thickness of the pad, how it “feels” and affects the feel of the mattress, its relative moisture resistance, care instructions, and how it may compare to other options you have available because there is a considerable range of options and prices for products that on the surface appear to be similar and are not easy to differentiate based on a basic description.
Based on the limited research I’ve done you should be able to find a combination that will work well that is in your budget range (depending to some degree on the size of your mattress) even though higher quality natural and organic fibers are typically in higher price ranges.
Hopefully some of the members here that have used a similar combination to what you are considering (a stretch cotton protector and a wool puddle pad) will see this thread and share their thoughts and feedback about the ones they purchased.
Phoenix