@janbb is correct. Hitting “Follow Question” will keep the question in your “Activity for you” until you decide to click the “Unfollow” button.
If there are new responses on these questions, they will show up at the top of your “Activity for you” list as “New activity”. Once you read the thread, it leaves the New activity” list, but it’s still in the “Questions you’re following” list on that same page. There’s no way for you to bump questions to the top of either list, but you can still scroll through them to find one that you want.
Alternatively, in terms of non-Fluther options, you could bookmark a specific question on your browser, or keep a list of links somewhere to refer to later.