To me, the font size should vary. A fairly large one would indicate when a stroke or two would be hard while the smaller ones would indicate softer ones. Also having several of them would indicate the speed. For example it could look like this: "Splish, splish, SPLISH, SPLISH, splish." or "SPLISH, splish, SPLISH, splish". Bold being the hard strokes. Also, having more than three onomatopoeias (Words used to indicate sounds), gives the idea of how rapidly Myriam is getting fucked, for example something like this: "Splish-a, SPLISH-A, splish-a" or "PLAP-plap-plap-plap-PLAP." Now you could imagine more clearly how fast and hard a guy would be thrusting.
I've been writing a somewhat extreme sex novel on Discord about a young, Afro-Latina woman who was once a stripper but is now doing concierge porn. I've sent excerpts to a couple of old gaming partners, using that style, and they told me that those excerpts were some of the hottest storylines that they had read.
Kthulhu, you could try it in a three or four panel scene to look back on and see if it would work for you.