This slides on the end of Dr Brown's baby bottles and gives a little nub to put in your mouth and stabilize/hold the bottle, freeing up your hand to google “how to swaddle newborn” or “how to soothe newborn” or “why does my newborn keep crying even though she's fed, changed, the right temperature, and being held?  she has everything she needs and I'm so tired…”

v2: I dropped the side nubs, made the end nub a little longer and give it a flat bottom (so that you can set the bottle down).  

v3: I reshaped the nub to be more stable/flat.  I added threads to the cup and the nub so they can print separately (shouldn't need supports). I had to print the nub at ~95%, but on a better calibrated printer, yours might just fit.