They don't make thicker ones, and stacking them is not advised.
Plus unless you have a 2000, the stock pistons don't like a lot of boost. Many pre-2000 engine have had cracked ring lands due to the earlier design.
Forged pistons are the way to go.
2000 SVT Turbo 295hp/269ftlb@12psi
#1 for Bendix Brakes Kits!
Knuckles rebuilt w/new bearings $55
AUSSIE ENDLINKS $70
Gutted pre-cats $80/set
A lack of planning on your part does not constitute an emergency on mine!