You might try spraying your doll with “Jell-coat” a 2-3 good, thick coats should do then fiberglass over that to make your mold.
Make sure you wax/mold release your latex doll before hand, (may not need to do to much with latex) experiment..
To separate the mold, attach some 1x2 wood strips with boltholes drilled through them (to attach the halves after the cut) then use a thin saw and cut your mold in half. Cutting through the attached 1x2’s. Use your bolts to make the halves whole again
You can see an example of this type of mold at
www.geocities.com/gr8_55/Armrest.html
If you get any pinholes, or larger defects, (in your mold) they can be filled with auto body filler.
Once you have that mold working, you could make several dolls