Advice needed, interior trim of adjacent windows and transoms
I have 2 sets of windows (3 adjacent double hung, and 3 adjacent double hung with 3 transoms). They are not factory mulled. They are anderson 400 series. The space between the windows is 5 inches which would work well to run back to back 2.5" colonial casing between all the windows/transoms. The problem is that all of other windows in the house and room are with 3.5" colonial casing. My only other option I have in mind is to run flat trim board in between all the windows. At 5" wide it could look dull, also it would need to be only 1/4" thick, I'm not sure if this is a common trim board thickness.
The walls are plastered around and in between the windows flush with the face of the windows. Any suggestions on how to trim and interesting profile in between these windows?