@TinyHouse4Life maybe a springform type but then finding a good way to size the bars would be tricky. The problem is you need flexible sides or something to get the block out. It rarely just pops out. In the past I've tried making a loaf mold with wood, but I had to disassemble it to get soap out.

I just found this wood mold on brambleberry that has a slide out removable bottom which might work (looks easy enough to build on my own). they also sell a silicon liner to make it easier to remove from the sides which I might buy.

https://www.brambleberry.com/shop-by-product/molds/wood/5-lb-mold-with-sliding-bottom/V000451.html

https://www.brambleberry.com/shop-by-product/molds/silicone/silicone-liner-for-5-lb-wood-mold/V000716.html

If I buy the liner I don't even have to measure to build the box around it. Having the removable bottom is a good idea. The problem with my pure silicon mold is that the sides are too flexible and the top is always pushed out from the bottom. A wood frame around silicon should address that. That was what got me thinking I might just be able to build a frame for the mold I have now. I think maybe that makes the most economical sense. I have lots of wood and I don't even need to worry about what species I use if it's just used to shore up the silicon mold and never touches the soap.