All the attempts in this direction that you describe have more or less failed. But of course you are right in principle.
The only material I know of with practically no material distortion is Soft-PLA.
I am now trying the glass plate as a rigid intermediate layer, let’s see how that works. This is the first attempt at my design, where the glass plate is glued to the flexible metal plate with adhesive tape. I don’t yet know how this adhesive strip will behave. It is important that the glass does not slip. I have applied the Cool Plate sticker to the glass, partly because the glass is a bit smaller. I set the bed temperature to 50°C and switched off the AUX fan manually.
Addendum: However, I have already taken similar or the same measures with the print that can be seen in the pictures (AUX-fan off etc.). So at least I was able to finish this print, even if it’s not pretty.