I use the app.
I use 'watch thread'
It's shit, you still have to trawl for miles to see where you are up to.
BUT
thanks to a darling poster who's name escapes me I've just read:
Swipe left on the last post you read, then when you return to that same thread - it takes you back to exactly that point 
*
- Used in conjunction with 'watch thread' is going to be life changing. I'm genuinely, unapologetically thrilled
I love the app but this is one of the things I moan about.
If everyone already knew - sorry, and why the fuck hasn't anyone flagged it before for a Luddite like me.