Hi JB,
Your questions are very broad and subjective so there is no way to really answer them with any degree of specificity.
There are no consistent standards between the firmness ratings of different manufacturers and different people will also have very different definitions of what feels soft or firm to them so the only way to know how soft or firm a mattress will feel for you is based on your own testing and experience regardless of how soft or firm it may feel for someone else (see post #2 here).
I would probably start by asking yourself “why” you are looking for an “organic” mattress or materials and why it may be important to you because in many cases people that think they want organic materials are really looking for “safe” materials and these are two very different things. Post #2 here has more information about the differences between organic, natural, safe, “chemical free”, or green materials (which all have different meanings) that may help you to narrow down which materials you are most comfortable having in your mattress or can help you answer the question “how safe is safe enough for me?”.
There are hundreds of people who have purchased a mattress from one of the online members of this site and been very happy with their purchase. A forum search on any of them will bring up much more information and feedback about each of them. None of them add any chemicals to their mattresses (and most other manufacturers don’t add chemicals to their mattresses either). When you can’t test a mattress in person then one of the most important parts of a successful online purchase is a more detailed conversation with any of the manufacturers or retailers you are considering (see mattress firmness/comfort levels in post #2 here).
This again would depend entirely on the person and on the specific mattress they purchased. Some latex is much softer and some is much firmer and you would sink in more with a softer latex mattress than a firmer latex mattress. Whether you “like” or “dislike” the feeling of any specific mattress or material would depend entirely on your own personal preferences because one person that would say a mattress has a “good kind of sinking feeling” may completely disagree with someone else who would describe the same mattress very differently. These are all questions that would be best answered based on your own individual perceptions and testing.
I think that one of the biggest reasons for the existence of this site is to help people realize that “you get what you pay for” isn’t always the case and sometimes it may even be the exception depending on which manufacturers or retailers you are considering or dealing with. There is more about the most important parts of the “value” of a mattress purchase in post #13 here than can help you make more meaningful comparisons where you won’t have to use price alone as an indication of the quality, comfort, or value of a mattress.
If you follow all the steps in the tutorial post one at a time (without missing any) you will have the best possible chance of making a successful purchase.
Phoenix