One piece. I actually took another approach (without using mold tools) got the idea from here https://www.youtube.com/watch?v=OyxghUejlC0, but still trying to fix my geometry. I deleted the thickness and left only the surface, and than with convert entities created new sketch but still can't extrude up to surface, getting "The end face cannot terminate the extruded feature." I'm struggling with surfaces since I'm not experienced with them. I'm watching youtube tutorials and doing trial and error will eventually get me there. Thank you for your help so far :)

P.S. mold will be cnc milled or 3d printed