Standard "tried searching" but no luck, so my apologies if this has already been covered.
Is there a swipe/action that I'm not aware of on iOS that gets you back from a single thread to the list of threads that's easier to reach than the "<" at the top left of the screen? Out of muscle memory/habit I keep swiping from the edge of the screen thinking this will take me 'back', as it does in many other iOS apps.
This makes single-handed use quite difficult, often requiring reachability to pull down the top of the screen. If it doesn't exist, this is my vote for most desired feature in the next version