Hi ydelle,
In most cases … an all latex mattress generally does best with a rigid non flexing slatted foundation with slats that are no more than 3" apart (and preferably less). In some cases thinner latex mattresses are made and designed as part of a “sleep system” and have either a box spring with flexible coil springs or torsion springs (such as the flex steel foundation) or flexible slats underneath them and these can change the feel and performance of the mattress because they add extra “give” under the mattress so if you test a latex mattress on one of these and it works better for you in terms of PPP (Pressure relief, Posture and alignment, and Personal preferences) than the same mattress on a rigid non flexing foundation then I would use the one that that worked best in your mattress testing.
As you can also see in post #10 here … I (along with latex mattress manufacturers I have talked with) also have some hesitations about the long term effects of using a wire grid foundation under an all latex mattress because the wires have less supportive surface area than a slatted foundation and there could be a long term risk of the flexible latex sinking into the gaps in the wire grid or the wires impressing into the latex.
The first post of this foundation thread and post #2 here has more information about box springs and foundations and which types generally do best with different types of mattresses along with some good sources for foundations if you are looking for an alternative to what the manufacturer of your mattress recommends. If you do decide to go in this direction though make sure that the foundation you choose is both suitable for our mattress and meets the warranty criteria of your mattress manufacturer.
Phoenix