Hi rvw,
Unfortunately looking at mattresses online is unlikely to ever get you closer to deciding on the best mattress for you because you won’t be able to tell which is a suitable choice for you in terms of PPP or which materials you may prefer. You may have read this already but just in case you haven’t … the first place I would start is the tutorial post here which has all the basic information, steps, and guidelines that you will need to make the best possible choices. Once you’ve read some basic information about mattress materials that may interest you and what to avoid (steps 1 and 2) then only your own personal testing will be able to “translate” all the information into your own personal experience so you can “feel” what you are reading about.
Post #2 and #3 here include the better options in your area I’m aware of. You would need to call them to find out which of them sell latex mattresses and which ones will provide you with the information you need about the materials inside their mattresses (see this article).
If you are planning to design your own DIY mattress (vs an online component mattress which already has a proven design) then I would make sure you read post #4 here and the links in option 3 first to make sure you have realistic expectations of success.
The best approach for a DIY construction is a “spirit of adventure” and a willingness to experiment through trial and error and what you learn along the way and the rewards of the process itself are more important to you than any cost savings (which you may or may not realize).
Phoenix