I would recommend searching through the archives - when the search engine is working – and see what others (who are smarter and more experienced than me) say on this subject. There are some really good discussions on this subject.
Best I can remember, it was just straight WW fluid. That is what I plan on using. As far as environment friendly, I think it's the "least" of the evils. Given what is required, won't freeze, prevent rust, etc., I think all fluids will have some chemical element that will have an impact.
I am staying away from auto anti-freeze because of environment, pet concerns and cost. It’s suppose to be among the best. Really prevents rust and won’t freeze, but, I can’t chance a leak and my buddy, Weaver the lab, getting into it. Calcium Chloride is suppose to be good as well, but, can cause rust if not maintained – see the referenced post above – I want low maintenance. There is a “beet juice” derivative that’s suppose to be very enviro friendly, but, I did not have any luck finding any and think it’s pretty expensive.
There was a posting once about a process that used a small “hard” material, almost like sand, to weight the tires. Was total enviro friendly, non-toxic and did not cause rim rust. But, it was not a DIY process and expensive. I could not find anyone local, within 100 miles, who did this. Think the nearest one was in TN/KY which might work for you.