how much can you compress a solid? Is it 2% heavier or 100%? How much can you compress a solid with explosive lenses?
"How much" is the wrong question, because the answer is too easy: you can compress a solid as much as you like. In the center of neutron stars the material is compressed to a tiny fraction of its normal volume, and in black holes it is compressed to what seems like a no volume at all.
What you think of as a solid is not really very solid at all. Most of it consists of the empty space between atomic nuclei. It seems solid because the electric field between the atoms holds them rigidly in place, and if you try to compress it the repulsive forces try to push the atoms apart and oppose the outside pressure.
However, if you apply unimaginably high pressures you can overcome the repulsive forces between atoms and force the nuclei together.
In the normal way, the relationship between pressure, volume and states of matter is called a phase diagram. Solids at earth scale high pressures can have interesting phase diagrams with different arrangements of atoms giving different crystalline forms.