Hi poppyone,
The overviews have more about the different materials that are used in mattresses.
Memory foam is too soft to be used as a support core in a mattress but there is a comparison between latex support cores and innerspring support cores in post #28 here. There is also more about the pros and cons of latex and memory foam comfort layers in post #6 here. In the end though there are so many variables and different versions of each material or component and so many different mattresses in each mattress category that these are just generic comparisons and your own testing is the only reliable way to know which type of mattress or materials you tend to prefer.
That would depend on which specific mattress you were considering and the materials inside it but outside of being able to say that most Tempurpedic mattresses use good quality materials (and have poor value) there isn’t much no.
There is more about the Casper mattress in post #2 here and in post #3 here and some more detailed information about Saatva in post #1 here and a forum search on Casper or on Saatva (you can just click the links) will bring up more information and feedback about both.
The “value” of the other mattresses you mentioned would depend on the specific mattress, whether they are a good match for you in terms of PPP, on the materials in the mattress, and on how they compared to other mattresses you are considering based on all the criteria that are important to you. The name of the manufacturer isn’t an important part of the “value” of a mattress and most manufacturers make a range of mattresses so it’s always important to look at mattresses on a mattress by mattress basis based on your testing and on what is inside them, not the name of the manufacturer (see post #5 here).
Post #3 here and the adjustable bed thread it links to has more information about adjustable beds and some guidelines that can help you choose the one that has the features that you are most interested in if they are an option that you would prefer.
This is answered in the previous post I linked in my previous reply about the most important parts of the “value” of a mattress purchase but this is exactly why in addition to testing a mattress for suitability in terms of PPP it’s important to know what is inside it so that you can confirm that it uses higher quality and more durable materials that won’t soften, sag, or break down prematurely. The post about the “value” of a mattress purchase also includes this link to the foam quality/density guidelines I would use and this link which has much more information about the many variables that can affect the durability and useful life of a mattress relative to each person.
Your best chance of making a successful purchase is following the steps in the tutorial post one step at a time but once you have done some basic reading and decided on your budget and the types of mattresses and materials you would like to test (steps 1 and 2) … it will come down to finding more open and transparent retailers and manufacturers (step 3) where you can test mattresses for suitability (PPP) and check the quality of the materials for durability and any weak links in the mattress (step 4), and then compare your finalists for “value” based on all the parts of your personal value equation that are most important to you (step 5) 
Phoenix