Techno, don't mix it using only the thiosulfate - it degrades very easily with free sulfur being a result. You should always have at least some small amount of sulfite ion in there to protect it; by some magic of chemistry, the sulfite and sulfur will recombine back into thiosulfate, restoring the original amount.
Kodak F-24 uses a mixture of sodium sulfite and sodium bisulfite, probably to control the pH; this is the simplest "official" formula I know of. (And it's in the link Matt pointed to.)
In his book, The Print, Ansel refers to what he calls "Plain Hypo Fixer," consisting of "Sodium thiosulfate (hypo)" at 240 grams per liter, plus sodium sulfite at 30 grams per liter. I just don't consider this an official formula.
In case you don't know this already, many people consider sodium thiosulfate fixers to be marginal with respect to so-called modern films, those containing some silver iodide. Generally, ammonium thiosulfate is recommended as the fixing agent for these. Hope you have fun with your experiments.