It is possible to get a COVID antibody test to determine whether you personally have sufficient remaining antibodies, or would benefit from another vaccine. In Barcelona, it is possible for under 100 euros.
There is no evidence-based clinical standard to determine what level of antibodies is "sufficient". Such tests are not useful for most patients and fail to account for cellular immunity. I am not discouraging anyone from getting a booster but the timing should be based on other criteria.
https://peterattiamd.com/covid-part2/