So after trying (and failing) a few different butterfly patterns, which were too small, had two sets of wings or wouldn't lay flat, I finally wrote my own pattern. The pattern I wrote uses a very similar technique to this pattern which was too small. (Note: the original pattern is on Ravelry so if you're not a member you may not be able to access it)
Using an I/9 (5.5mm) crochet hook and worsted weight yarn
Make magic loop, chain 3,
Rnd 1: Dc 12 in loop, close magic loop, Do Not join, ch 3, turn, (12st)
Rnd 2: Dc 2 in each dc, Do Not join, ch 3, turn, (24st)
Rnd 3: (dc 2 in nxt st, dc 1) 12 times, Do Not join, turn, (36st)
Rnd 4: *sk 4 st, dtr 9 in nxt st, sk 4 st, sl st,* (sk 3 st, dc 9 in nxt st, sk 3 st, sl st,) twice, repeat once from * to *, tie off, (if you leave this tail long you can use it sew the butterfly on)
Antenna: Sl st in 2nd sl st of rnd 4, ch 3, sl st around 12th dc of rnd 2, ch 3, sl st in magic loop, ch 9 very tight, ch 1 very loose, ch 9 very tight, sl st in magic loop, tie off, weave in ends, cut the loose ch, pull out short threads, pull others tight and cut them to be the same length.