These TPUtform Shoes are 3D-printable, flexible sandals using TPU.
Designed for a women's 7-7.5 foot, but can be scaled up or down!
The platform part of the shoe is the 3D-printable component.
Then, you can weave the straps through the slots on the side of the shoe, hot glue them to the sole, then create a leather sole out of hot-glued thin layers of leather or pleather.

Necessary extra supplies (all available from Joanne Fabrics):
Thick leather strap, 1.5" wide, 1.5 ft long
Stretchy fabric, 1.5" wide, 1 ft long
Leather or pleather cloth (1/2 square meter)

I've also attached the STL file for a Ninjaflex insert. If you can print Ninjaflex and would rather not make the leather sole, then try this out!

Final note: these shoes are squeaky on concrete so I am working on attaching some material to the bottom (leather, rubber, etc.) to dampen the sound.