It doesn't have to be a solid. A tiny print or something that "reads" as solid to separate the stacked coins into panels.
Another idea is stacked bricks. You would sew your 3.5 x 6" pieces end to end in horizontal rows and off set each row so it looks like a brick wall.
I got a newsletter from epatterns this morning that has a design in it that might work for you, also. It's a cross between rail fence & garden path.
http://www.e-patternscentral.com/det...ng+Garden+Path
If the link doesn't work, to to
http://www.e-patternscentral.com and search for Spring Garden Path. I don't see paying $3.49 for the pattern, though when it's so simple to figure out but it might help clear your chemo fog.