This topic has been covered before, however after my car since March ( 8k ) I finally decided to get my a into g.
As I like and wanted to retain the flat boot liner, this is what I came up with.
I obtained a space saver wheel off a Sub Impreza 06/ 07, Part Number T135/70 D17 off Sunspares Yandina ( Subaru Wrecker )
Then ordered from Toyota SU00303404 and a SU00304451 Bolt and Washer to bolt wheel into boot well ( as covered by an earlier thread. Thankyou very much )
So into the shed and found a bit of 18mm marine ply and cut out with a jig saw an 460mm dia.
I then used a 10 x 12mm blocking rubber to raise the new floor up to be level with the rest and screwed this to the underneath .
This then sits on top of the spacer saver wheel inside the boot.
I will be taking out for a test drive soon to check for any rattles.
Test drive done and no rattles present
The blocking rubber available from Glaziers and glass companies was perfect as it was easy to mould around