It is a lovely print and I'm glad you left it whole!
How about outlining each butterfly?
Then do a loop-de-loop meander to the next one.
You could even toss in the odd daisy on the loops between.
Plus, it'll give a nice design on the yellow.
For thread, I would look for a pale variegated that coordinates.
It won't be too noticeable and might blend a little nicer around the butterfly edges, than a plain white.