I have the same problem. I know what you mean about a floater that doesn't seem to move when you move your eyes quickly. I have hundreds of floaters. When I move my eyes, some of the floaters move exactly with them, some lag behind the rest, some keep floating on after my eyes stop, some are like strings that are attached at one end, so they move differently, depending which way I move my eyes.
I remember having floaters since I was about 12; about the same time my eyes started getting bad. I'm near-sighted. In the beginning, they were small and unnoticeable except against very light backgrounds. By the time I was 20, there were a lot of them and I had some pretty big ones that were noticeable all the time except in very dim light. After that, I didn't notice any big change until I was 38. Then all of a sudden I got two really big ones (one really gigantic) and a smaller dense one within a year. I'm 42 now, and haven't noticed any big change since then.
I've talked to optometrists about this several times. They always say it's normal for near sighted people and nothing to worry about. One told me the floaters are tiny (almost microscopic) pieces of tissue that break loose inside a small, gel-filled disk that covers and protects the retina. They only appear bigger because they're so close to the retina. That's also why there is no treatment yet (last I heard). You'd have to rupture the protective disk and extract nearly microscopic bits of tissue within millimeters of the retina. It's just not worth the risk for a simple annoyance.
Personally, I hate them and would almost be willing to risk blindness to get rid of them. I'd pay $1000 just to get rid of the one that jerks back and forth over the words when I read. But the problem is not debilitating and apparently doesn't lead to anything more serious. And the optometrists seem not to care about it at all. I suggest doing what I do. Just try to ignore them and don't worry. But ask the optometrist every time you get your eyes checked if it can be corrected. Maybe if enough people ask, somebody will develop a treatment.