I got these spa slippers. Weight 4.2 oz for the pair! Pretty good grip. Comfortable. Can you just glue a piece of light foam to the front to close them in? Maybe even a netting/fabric to look like they are closed.

Also they are less than $10. Can't beat it!

https://www.amazon.com/Jiyaru-Unisex-Anti-Slip-Slipper-Indoor/dp/B01A50I43E?th=1&psc=1