Using velostat instead of a force sensing resistor
My experience with Velostat is somewhat poor.  I find that the force/resistance relationship is much more sensitive to the physical connection between the outside conductors that sandwich the sheet, almost going away if I used conductive adhesive to glue the sheet down.  The piezoresistive component is much smaller than you would think.

If you want to design your doohickey this way, try to get the interface between velostat and metallic element to vary reproducibly with pressure.