I have done it with bias edges, and as long as you are careful pressing, it's not a problem.
I seriously do not understand why so may people think bias is something to be afraid of and avoided.
The border (inner and outer) was done with ombre fabric cut on the bias and there are no waves in it. And I do not use starch so it's very possible to do. I rarely worry about the bias edge on any setting triangle. I don't think I've ever cut super large squares and cut them double.
