Hi Bobbi,
The foundation thread here should be helpful 
The PJ’s organic foundation would certainly work well and have 1.5" gaps between the slats.
They will fit a standard metal bedframe yes.
If you have a bedframe with wooden slats I would probably make sure it has 5 slats in it and a midbeam supported to the floor for strength.
You can see my thoughts about the stand alone wire grid foundations in post #10 here.
Just make sure it’s the organic if you decide to purchase from PJ’s (see this thread).
Phoenix