Would something like THIS work?

Rub them on rough concrete or use a 50 grit sandpaper. Put a coating on them of grip stuff. I usually just rough them up on concrete. Obviously you've tried that though so YMMV. Good luck.

Make-Shoes-Less-Slippery

Try scuffing the soles (as above) diagonally or crossways, not in the front to back direction along the length

Target has things to put on the soles.

If you have a tube of silicone left over from a bathroom caulk project, you can put a bit of silicone on your slippers.

I have no ideas but remember whatever you do needs to be safe for hardwood.

Shoe carnival sells little things for slippery soles. One expensive pair of boots I have, were almost unuseable because the soles were so slippery. These little things are self stick, and can be cut to size. I now wear the boots all the time.

I have used the non-skid, stick-ons, for the bathtub. They can be cut to the size you need, and stuck on the bottom of the shoe. Worked for me.

Thank you all! Lots of good ideas. I'm thinking the silicone would be good; it dries a little 'tacky', so it shouldn't hurt the floors. The bathtub stickers sound good, too. Now...I just have to find the 'makings'.

Oh! Just this moment I remembered that I have a can of spray that I've used in the past to renew the rubberized side of a bathroom rug. (I don't buy that type anymore *because* the rubber shreds in the wash.) Maybe...

Anti-Slip spray. Rust-Oleum, Krylon and several others.

Here's one specifically for shoes.

Shoe Spray

I use the Krylon on my cell phone case. Never dropped yet.

Thanks, Brushworks. Bet I can find that at the hardware store.