Check out this responsive (mobile, small, medium breakpoint) and fully customizable variable grid post layout! You can add as many settings for each breakpoint as you want, it will repeat the settings until it runs out of posts!
Make sure to set the items in groups so that they sum up to a full row.
1-2 + 1-2
1-3 + 1-3 + 1-3
1-3 + 2-3
2-5 + 3-5
are all good examples of such groups.