I use custom sunglasses, first sourcing suitable frames when necessary (I prefer "glacier" glasses, but some wrap-arounds are ok), then getting the optometrist to tint the prescription lenses to +95% black/grey. I've had them done without fuss in Bendigo and somewhere in NSW (years ago, cant remember where), and again recently out gippsland way, though they had to be sent off, apparently not many do that sort of thin "in house" any more. Ask at the optometrist where you intend on purchasing sunnies and find out which have Rx lenses and can be tinted further.

Keep in mind this rules out proprietary treatments and polarization etc (from what I was told).

I'm not too familiar with the categories (in Canada, we use the percentage of light transmission). But check into the Noir brand. They sell fitovers that are pretty strong, and have a few different colours as well. I'll post a few links but that isn't exhaustive.

https://shop.cnib.ca/ProductDetail/sun3115020750_noir-u30-uv-7-grey-green-sunglasses
7% light transmission

https://shop.cnib.ca/ProductDetail/sun3138010460_noir-l23-uv-4-dark-grey-sunglasses
4% light transmission

https://shop.cnib.ca/ProductDetail/sun3148090260_noir-907-2-dark-amber-sunglasses
2% light transmission

https://shop.cnib.ca/ProductDetail/sun3148020150_noir-708-1-dark-grey-green-sunglasses
1% light transmission


One thing I should mention, depending on what kind of glasses you wear, you may have to get a really large one. My glasses stick out a bit, and even with the largest set, the corners of my glasses scratch the inside.