When I looked at the striped quilt that you initially liked I could see your concern. It does look like two twins sewed together.
How about you do 4 panels. HAve the first one on top go horizontal and the second top panel go vertical.
Then on the bottom reverse it. Left panel is vertical and the second is horizontal. ( see my pitiful diagram at the bottom of this post)
Make your panels 42 X42 and when they are sewn together they make a quilt 84X84 (approx). A good size and you do an modern stripe quilt without the problem you see in the first one.
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