Hi rlk,
I don’t think there is any doubt about the benefits of inclined bed therapy for those with medical issues that would benefit from it and thanks for bring up the subject in the forum 
This thread is from another member who mentioned it as well.
Some of the benefits would be similar to having an adjustable bed but the advantage of having an inclined surface from top to bottom rather than just the top part of the bed is that you can sleep on it in any position while an adjustable bed that has the head raised slightly is limited to back sleeping. It would also have a much more even incline that a typical wedge that only raises the upper part of the body.
A quick scan shows that Simmons also has a wedge topper (among othes that do as well) that performs a similar function made from polyurethane (although it doesn’t say the quality of the polyfoam) but it would be less durable than latex and have a greater effect on the feel of your mattress being on top instead of the bottom. Used on top it probably also wouldn’t provide the same type of even incline or alignment as an inclined wedge on the bottom of your mattress which wasn’t part of the actual comfort layer of the mattress. Of course it could also be used under a mattress.
There are also some inclined beds available such as here that have a similar function to the full body wedge you are considering and these have the advantage of being able to adjust the degree of the incline.
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There are also many discussions around the web about inclined sleeping for those who want to do more research including a forum here with a number of threads that mention it (and there are others as well).
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Talalay latex is a high quality material and very durable so it would make a good choice for a full body wedge but I would use it under the mattress rather than on top. I wouldn’t consider it as a layer that will affect the feel of the mattress as much (I would leave that to the mattress design itself) because you will only feel it’s properties through the mattress itself and the further away from a layer you are the less it will affect how the mattress feels in most cases (although this will also depend on the specifics of your body type and sleeping positions).
Putting a foam wedge on top of a mattress where it will have a larger effect on how your mattress feels may also have a negative effect on spinal alignment.
I know this is a much larger topic but I thought I’d include a few links to add to yours for those who are interested and hopefully there are other forum members that have some experience with inclined sleeping that can share their feedback.
Phoenix