Hi noaries,
If the box spring you currently have is a wire grid type something like this or like this … then it would probably be fine for the short term (and some people would say for the long term as well) although as you can see from this post I have some mixed feelings about them.
If your box spring has actual slats that go from the side rails to a midbeam and they are 6" apart something like this or the support surface has similar gaps, then I wouldn’t use them even for the short term without a foundation or other type of supportive surface over it because they are not close enough together IMO to prevent the latex from sinking into the gaps.
Plywood would also be fine in the short term although it’s also not a good long term solution IMO because it doesn’t allow ventilation between the mattress and the support surface which increases the risk of moisture buildup and the dustmites, mold, and mildew that can go with this.
Phoenix