Hi Nirvana,
Thanks for the post, I moved it into the General Mattress Questions,
A latex mattress needs just a solid base with enough supportive surface to make sure that it doesn’t sink through any gaps and that the base is strong enough and supported on the floor well enough to take the weight of the latex mattress and the people that sleep on it. Normally this means that a slatted wood or even a metal base would be the best. Both of these are rigid non-flexing bases. The characteristics of the box spring are typically designed into the overall sleeping system itself and are an essential part of how the mattress is designed to perform in terms of pressure relief, alignment, and overall feel. In these cases, it is just as important as the mattress itself to achieve the design goals of the sleeping system. This would have more give under the mattress and can also be designed in many different ways to change the way the mattress feels and performs. As you got the go from Plush to use the boxspring you may wish to see how the entire system performs for you before moving in a different direction with the foundation. You can read more about foundations in post #1 herehere or post #2 here about old box springs under a new latex mattress.
Please check out our trusted members, we have many companies that have sold quality latex mattresses for many years and can recommend something for you.
Thank you,
Sensei