Strong mold material ideas

I’m totally new to mold making. I’m interested in making molds which will then be used to create “compositional ornaments” for picture frames that I make. “Compo” is a dough like material which needs to be firmly pressed into a mold, in my case I would be using a hydraulic press to press the compo into the molds. Once pressed, the compo is flexible enough to be removed from the mold without much effort.

I intend on making the molds in wooden boxes for reinforcement (in which they would stay) and need a mold material that is high in strength and can keep all of the fine details after many castings, and which won’t crack under the pressure of the hydraulic press (I won’t be using too much force, but it would still be upwards of 1,000 lbs or possibly more). The molds themselves wouldn’t need to be more than 1 or 2 inches thick as the ornaments themselves are very thin.

Is there a type of silicone that would work for this mold making or do I have to explore other options? Traditionally compo would have been pressed into metal or wood molds, but these are prohibitively expensive and I do not have the skill to carve them myself.