Regular bathing of feet in vinegar. Add a little salt and warm water if you want, for that wonderful fish and chip smell. Bathe for 15 minutes or so and then dry feet, do not rinse off.
The idea is to change the climate adversely with respect to fungal infections not just on the surface but allowing it to get into the skin when your feet are immersed for some time. It’s worth applying pressure to toenails to try and suck some under the nails a bit too.
Vinegar is very very cheap – do it daily until signs of improvement and then a bit less frequently for a period afterwards. This has cleared up cases for me that did not respond to expensive powder and creams.
This advice came from a doctor. It works for me. And I believe the Romans! Been using this method for some years when needed. You can also use it as a preventative as it does not favour the organisms that cause it.