Hi balan,
You are in a very low budget range for a latex mattress of any kind … especially if you also need a foundation … but the better options and possibilities I’m aware of for latex or latex hybrid mattresses that are in lower budget ranges are listed in posts #3 and #4 here.
Whether it’s “OK” or not would really be up to each person based on the criteria that are most important to them. All the latex you will encounter whether it’s Dunlop or Talalay and made from natural or synthetic rubber will have been tested for harmful substances either by Oeko-Tex or Eco-Institut so they would all certainly be safe (see post #2 here).
As far as environmental issues, natural rubber will probably oxidize and break down more readily than synthetic rubber although vulcanized rubber of both types are more difficult to break down than rubber that hasn’t been vulcanized because of the cross linking that is the result of the vulcanization process and it would also depend on the amount of antioxidants and antiozonates and other “anti degradant” substances that are added to foamed rubber to prevent it from breaking down prematurely.
As far as performance … the synthetic continuous pour Dunlop that is being made by Mountaintop foam is a high quality product that is very durable but synthetic rubber isn’t as elastic or as dense or “supportive” as 100% natural rubber that is in the same ILD range and it will have a different “feel” from 100% natural Dunlop although it’s also less costly (see post #6 here). There is more about the different types and blends of latex in post #6 here and more generic information about some of the differences between natural and synthetic rubber in post #2 here but the compounding formula will also make a difference in the feel and performance of latex. Synthetic latex is certainly a higher quality and more durable material than most polyfoam materials.
There are certainly some memory foam products that sleep cooler than others and this has been a significant focus in the memory foam side of the industry. There is more about some of the different technologies that are being used to “cool down” memory foam in post #6 here. And there is also more about the properties of different types of memory foam in post #9 here and in post #8 here. In very general terms … higher density memory foam will be more durable than lower densities up to about 6 lbs density or so and I would tend to avoid memory foam that was less than about 4 lb density because of potential durability issues. There is also more about the many variables that can affect the sleeping temperature of a mattress (outside of just the type of foam it uses) in post #2 here. While most of the memory foam that is being used today will be a little cooler than most of the older formulations … in very general terms … and all the other factors being equal … latex is more breathable and will tend to sleep cooler than memory foam.
So called “soy based” foam is just polyfoam that has replaced a relatively small percentage of the petrochemical polyols (which is one of the two main chemicals that are used to make polyfoam) with an alternative polyol that is synthesized from soy oil. There is more about plant based polyols in post #2 here.
There is more about the differences between an innerspring support core and a latex support core in post #28 here and post #2 here. It comes down to a preference issue based on “feel” and performance rather than being a “better/worse” issue because the deeper layers and components of a mattress aren’t usually the weakest link in a mattress in terms of durability.
All mattresses will need a suitable support system of some kind yes but there are many different options. There is more about the different types of support systems that are generally most suitable for different types of mattresses in post #1 here and the posts it links to in the second paragraph.
The better options and possibilities I’m aware of in the greater Los Angeles area (subject to the guidelines here) are listed in post #2 here. You certainly have many good options in the area.
Phoenix