Hi Wavycat,
An all latex mattress will generally do best with a slatted foundation or base where the gaps between the slats are 3" or preferably less. If you use 1 x 3 slats then I would add enough of them so that there are no gaps wider than 3" to prevent the latex (which is very flexible) from sinking through the gaps over time (keeping in mind that 1 x 3 slats end up being 3/4" x 21/2").
The center foot should also be supported to the floor (with books or a 4x4 legs such as these) and two would be even better than one to prevent sagging in the middle of your bedframe.
Phoenix