I’d like my mobile design to have a single column of text and images, but larger designs to have two columns. Is the only way to do this to override the larger design, or is there another way?
Yes, the way to do this is by overriding the single column on the larger screen sizes, by clicking on the little dot in the left column, to perform the override. Then select the number of columns required for the larger size. All sizes above the overridden size will then inherit the number of columns, unless overridden.
Yup, @handshaper is correct, and check out this video to see how it works in action:
An alternative is to duplicate your container and style one with a single column and the other with two columns. Then, depending on your screen size, you can hide or unhide the relevant container.
I do this occasionally because it means I can add borders/dividers etc on the multi column layout which I don’t want on the mobile view and sometimes I have that many overrides going on I get confused.
Not sure if this is good advice or not but works for me.