I'll give this DU-member a clue for free. Get tested for anti-Covid antibodies. If the results are near or past the high end of what the test can measure, a booster is not needed and won't do much, if anything. I did that test (~$69) 6-7 months after my second shot of Pfizer (and ~11 months after recovering from Covid). My antibody level was higher than the test could measure, so I am unboostered. IOW, I did what I suggest, and plan to do so again at the appropriate time.
Reality is that besides creating antibodies, both recovery and vaccines also cause a B-cell response, the immune system's "long-term memory". So both are approximately equally effective in producing significant resistance, from antibodies and from the immune system "knowing" how to produce more antibodies. However, NEITHER create total immunity. IOW, whether recovered, fully vaccinated, or boostered, there is no zero-risk-of-getting-Covid option. And while recovery and vaccination both tend to make one less likely to have a serious case of Covid, endless boostering despite (or without) antibody tests is stupid and useless.