The sculpt will most probably suffer some damage anyway you mold it.
As for the resin and polyfibers can you get Smooth On products where you are?
Urefill 11 would be their polifyber version:
https://www.smooth-on.com/products/ure-fil-11/
As for the PU resins you could try several. I´ve made small molds (severed hand for example) with smoothcast 65D, which is nice working with ( gradual hardening), Ure-fil 11 and backed with fiberglass. But 65D is low shore plastic, so maybe to low for a head. Onyx is another resin to try, and you can always use fiberglass as a last backing coat.
Another option could be poliester+fiberglass or epoxy+fiberglass. The downside of these is that you will need (most probably) post curing, specially with polyester resin, as they inhibit plat silicone when freshly made. You need styrene to go away. Epoxy could be less problematic in that sense. I have molds of heads and others made in both materials, but post curing and tests are a must. Fast setting silicones also help to minimize inhibition.
More options:
Acrylic resin (Acrystal, Jestmonite etc...). Nice to work with (no solvents, no fumes). Works fine with silicone. You will need to make molds a bit thicker than resin+fiberglass ones.
Or ole stone plaster (Ultracal for example), which will do the trick, but heavier molds.