You can use all of them! In slightly different ways. If you're looking for a coursebook, Outcomes Upper Intermediate has a good section on vague language like this in unit 15.
So so (I usually use this when someone asks me how I'm feeling and I'm not feeling very good. I'll shake my hand and say so so. It means "not bad" or "ok". I usually only use it when I'm not ok but I don't want to say something negative)
More or less (usually I use this when replying to other peoples closed questions. "Do I need 500g of pasta?" "Yeah, more or less" and it means approximately. Another great phrase for this is "give or take"
Ish (not ich! You can add this to a time to say it's a approximate, for example "I'll meet you at 12.30ish" = about 12.30, but not exact. You can also add it to an adjective like "It's a greyish blue colour" = it's a bit grey and a bit blue