Hi Beth2014,
The foundations from SleepEZ and USBoxspring are the same foundation.
The USBoxspring foundation and the mattresses.net foundation both use the same wood (Spruce) and are fairly similar. The main difference would be in the cover with USBoxspring using an organic cotton cover with a quilted border.
You can see my thoughts about a wire grid type of foundation for an all latex mattress in post #10 here. While I would tend to use a foundation with more surface area for an all latex mattress … if you do decide to go in this direction and it does squeak (and most of them have some feedback about squeaking) then it shouldn’t be hard to fix the squeak either by tightening any bolts or with a washer or by lubricating any metal on metal contact points that are squeaking (usually in the folding braces). If you purchase one that doesn’t have a headboard attachment then they are quite inexpensive to purchase.
Phoenix