As a test, set the ski on 2 housebricks at the width of a mini. then stand in the middle. If it flexes , but bounces(oscilates) then it will be a bit flexible . If it bends 30mm and sits there then its probably just right.
take a photo

. then repeat the test with 2 skis clamped together.
You get very strange looks when doing this in a timberyard