How to pick the correct mat for Oracle Delphi

When I owned an Oracle I tried the same mats you mention plus the Linn, a glass mat, a glass and Teflon sheet combo and the Goldmund.

The Goldmund was the clear winner in my tests. I doubt it is still manufactured but likely one could be found used.

I thought acrylic mats were all the rage now. I have a Mk.2 Delphi as well and was wondering the same thing. It currently has its original mat.

I have used for many years on my Oracle the "Record Interface Mat". This is a solid polymethylacrylate mat made in the Netherlands by Audiophile Products Nederland. I bought mine in Holland and I do not know if it is still made.
I think it is the same mat as made for Goldmund. It is much heavier than the Oracle mat and you should not use it unless you have extra springs to retune the suspension of the Oracle. If you do it will increase the inertia of the disk and slightly lower the resonant frequency of the suspension, which are advantages in addition to having the damping of the disk changed.
The very best upgarde to an Oracle however, is to replace the bearing with a Perfectionist Engineering bearing if you can find one.