Turn on Maximum file size in Image Converter and set a KB or MB limit. Image Converter searches quality settings automatically, and can reduce dimensions too if you allow it, always deriving from the original image so repeated attempts never compound compression loss. If the limit genuinely can't be met without unacceptable quality loss, it tells you rather than producing a degraded result.
Image Converter can target a maximum file size
Set "no larger than 1 MB" and Image Converter finds the settings that get there, without you guessing a quality percentage.