There are a lot of molds out there that you can use for making your soap. I personally use a 5lb wooden mold but they can be expensive. If you're planning on making soap for your family for the rest of your life (that sounds like a long time!) or working into soap making as an income, then I'd recommend buying one. If you're just going to "try" making it and maybe aren't as interested in having soap making as one of your homestead chores, then I'd pass.
Plastic molds work too. They are less expensive than wooden ones. I've even seen folks use a plastic storage container or square plastic bucket for molding their soap. Make sure that your plastic is bendable though. When your soap starts to harden you're going to want to be able to pop it out of the mold. (Think getting ice cubes out of the ice cube tray.)
Here are a couple links for some molds:
You can google more if you'd like.
If you'd like to be frugal then go through your attic or your storage and find something that will work. You can also build your very own wooden soap mold. A friend of mine has her husband build hers and they are great!
Here are a couple links for making your own: