I've always considered couscous even softer than quinoa, especially regular couscous as opposed to Israeli coucous. Israeli couscous is bigger and rounder than regular couscous and tends to be cooked more al dente. Israeli type is also a toasted pasta. Both are forms of semolina wheat pasta and are not a seed like quinoa. Of quinoa, I found the white variety slightly softer than the red. I usually used only the red. I never bought the black variety, so can't comment on that.

As someone else mentioned, bulgur wheat would be another thing to consider, and can be soft if you cook it enough. Bulgur comes in various levels of fineness, with "fine", "medium", and "coarse" the most common. The preparation methods and times vary by fineness and all can be made to various levels of bite. Softer with longer cook time. Lentils, a type of legume, can share some uses as quinoa, but also has others. There are various colors of these, too, and firmness varies with type and cook time, as well.

I prefer quinoa and bulgur over couscous, personally, though quinoa has some uses less appropriate for bulgur or couscous. Depending on what you want to make, definitely also consider lentils. Red/yellow lentils are usually cooked to mushy. Brown can be al dente to mushy. Green are usually always used as al dente. These are the main types.

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