I can’t think of a way to automatically do what you want.
If you manually save the new address when you get to the end of a thread, that address should open up the thread where you left off.
For example, in this thread the last post of yours would be: https://broadbandbulletin.com/d/1579-site-suggestions/12
(Each new post adds 1 to the end of the address, but this might get thrown off kilter when posts are split off or deleted from the thread. You can see this in action by scrolling the thread and looking at the address bar change.)
