I got an adapter hose from co2 supermarket [0] that fits my local standards.
I also added a standard regulator to my setup because I trust it more than the sodastream, tho the pressure rating of the sodastream should be enough.
Then I got a tank of food-grade co2 from my local supplier. I guess welding grade co2 would be good enough as well, but as the price difference was non-existent it was a no-brainer.
When you get a regulator, make sure you get the highest flow-rate you can find as some of them will be problematic to get enough pressure for your beverage.
Mine does not go nowhere as high as the regular sodastream bottles directly, but the result is that it takes me an extra 10 seconds per bottle to get the same result.
[0] - https://www.co2supermarket.co.uk/adapters-for-co2-regulators...
