Hi KiminTN,
The fist place I would start in any search for a new mattress is post #1 here which will give you the information, steps, and guidelines you will need to make the best possible choices.
There are far too many variables and individual preferences involved to provide a single answer to your questions or have someone else answer which single mattress is “best” for you. You will need to do the research and testing that can answer these questions for yourself based on your own unique circumstances, needs, and preferences. As you will see in the linked post … who you “connect” with can be just as important as which mattress you are considering. As an example … post #2 here and post #29 here will help you learn about the many different factors that are involved in the sleeping temperature of a mattress so you can evaluate the mattresses you look at and are available in your area against the information there to give you a reasonable idea of how warm it may sleep for you (which may be different from someone else).
In the same way … questions about the safety of a mattress will depend on your answer to the question “How safe is safe enough for me?” because there is no one answer that fits all people, circumstances, or sensitivities. Post #2 here and post #2 here may give you the information that will help you in answering this question as well. Of course … connecting with the better informed and experienced manufacturers and retailers in your area can also help a great deal because they will likely already know what you would otherwise need to spend a great deal of time learning. Who you connect and deal with and their own knowledge and experience is the best “shortcut” that exists.
You can read more about waterbeds in this article.
Most of your other questions are either too broad or too specific to you to have any meaningful answers because you would first need to have a bit more context, testing, and basic information behind you. You are looking for answers that don’t exist to the level of specificity that you are looking for and that nobody can answer for you without your own research, input, and testing. I would first follow the first few steps in the first post I linked and then when you get to step 3 if you let me know your city or zip code I’d be happy to let you know of any better options or possibilities I’m aware of in your area.
Based on the questions you are asking … I don’t think you are close to being ready to order a mattress by tomorrow. A mattress is one of the most important purchases you will make and will have a significant impact in your overall wellbeing over the next decade or so and I would strongly encourage you to take a little more time to learn a little more and connect with some knowledgeable people to help improve the odds of making a good quality, good value, and informed choice that is suitaqble for your own specific needs and preferences…
One small step at a time 
Phoenix