I found my way back finally. Sorry, how rude of me to not finish the reveal. I can fix that...
I basted small off-cut pieces of batting behind each flower - I found it easier to baste with thread rather than pins so it was guaranteed to lay flat and smooth
and then free motion stitched a line close to the edges of the petals (aka raw edge applique) and also in the centre of the flowers. I stitched a spiral here but other flowers had hearts or pebbles stitched in the centre.
I then flipped the quilt top over and carefully cut away the excess batting as close to the line of stitching as I dared without cutting into the fabric.
I did the same for each heart and butterfly except for the three large hearts which were attached by needle-turn appliqued and have 2 layers of batting behind them for the trapunto. These were stitched close to the edge on the background fabric rather than on the applique fabric and I was really happy how they appeared to pop out of the quilt. I also used needle-turn applique to attach the caterpillar segments and added 2 layers of batting for the trapunto there too.
Then to finish off the butterflies I hand stitched the antenna with chain stitch, backstitch or stem stitch. The one above was done with chain stitch.