The crash sensor on this should be the same position as a MK5 Golf. (The Golf door comes apart differently though).
It should be on the window mech side of the N/S/F door card - unfortunately on Skoda these are riveted on, so make sure you order the rivets from TPS.
The sill / under the carpet crash sensor that AD is listing would be for a 1U chassis Octavia, not the 1Z you have.

I've sent you an email with some info.

Jon.