Why not use the breath mark that LilyPond uses by default, instead of
the textual comma sign: \musicglyph "scripts.rcomma" ?
Or simply "comma"?
\version "2.20.0"
breatheWithFermata =
#(define-music-function (offs) (number?)
#{
\once\override BreathingSign.Y-offset = $offs
\once\override BreathingSign.text = \markup
\override #'(baseline-skip . .8)
\center-column { \musicglyph "scripts.ufermata" \musicglyph "comma" }
\breathe
#})
{
c'2.
% construct the symbol
\breatheWithFermata #3.7
c'4
}
Cheers,
Pierre