There’s a professor and his research group at university of Michigan that does compliant mechanisms that u could check out if they’ve got something. It was a while ago that I applied there so possible he moved but still worth a check.

I’ve never used freecad as I’ve always had access to a cad program thru either school or work. One option that’s not free is to join a maker space that has better cad programs or just torrent. But you’re definitely in need of FEA for the bistable part