If you want to shrink then ATiny or Micro is probably a better place to start.
It would be easier i think to squash those down and still do what you are outlining.
The other benefit is that if you don't need a large sketch or lots of speed you could drop to the 3.3 Volt board with Lipo right off the bat almost.
Does the tiny have enough IO for your needs
Curie is 101 and 101 is Curie.