The answer to the question is something called an equity index futures basket.
S&P/Dow >>> 50*/ES+5*/YM
Nasdaq/Dow >>> 40*/NQ+15*/YM
Dow/Russell >>> 10*/YM+150*/RTY
You can use the same chart to buy or sell the basket.
You just go to the CME site, look up the margin credit ratio, and buy or sell both with the spread ratio to trade them as an index basket. This ratio attempts to balance the exposure between the instruments. It's based on weighting the exposure so that each leg contributes to the spread/basket evenly (in dollar terms).
Link
https://www.cmegroup.com/clearing/margins/inters.html#pageNumber=1
(edit)
Just my opinion, but the ratios on the site are not the final word on spreading these things. For example, you can spread two ES contracts against an NQ intraday. It has almost the exact same variance, but the position is better hedged.