Hi Kaye,
I’m not sure you are clear between the difference between a box spring and a foundation. A box spring has springs inside it that flex under the mattress and there are very few one sided mattresses today that use them as a support system and in many cases they will invalidate a mattress warranty. Most mattresses in the industry today need a steel or wooden bedframe with a foundation that has minimal to no flex (vs a box spring that flexes) or a platform bed which also has little to no flex under the mattress. There are many in the industry that mix up the terminology between box springs and foundations even though they are very different products.
There is more information about the different support systems (bedframes and foundations or platform beds) that are generally suitable for different types of mattresses and some examples of each of them in post #1 here.
An all latex mattress will generally do best with a firm, flat, and evenly supportive support surface underneath it that has minimal to no flex under the mattress and for larger sizes with at least one center support beam that has good support to the floor to prevent any sagging in the middle of the mattress. The components need to be strong and durable and stable enough to support the weight of the mattress and the people sleeping on it without some of the parts bending, sagging, or breaking over time. The support surface under the mattress should have enough surface area to prevent the mattress from sagging through any gaps or spaces in the support surface over time but still allow some airflow under the mattress. I would suggest that in a slatted support system (either a foundation on a steel or wooden bedframe or a platform bed with a slatted support surface) that any gaps between the slats are no more than 3" (with 1 x 3 slats) although less than that would be better yet.
A suitable foundation should not have any effect on the feel or durability of a latex mattress and should be very similar to having your mattress on the floor. If a support system (bedframe and foundation or a platform bed) does have an effect on the feel or durability of a latex mattress then with the exception of a few thinner two sided latex mattresses that are designed to be used on a box spring … it would be the wrong support system.
Phoenix