@seosamh…not telling you how to pronounce your own name, but I’d always say “Show-siv” i.e. pronouncing the “mh” as somewhere between an ‘f” and a “v”.
“Show-sa” sounds a bit like “Seoirse”, which is gaeilge for George.Depends where about in ireland you are talking about, very much a dialect thing I think, I’ve heard some say the V some not, so am aware of that. Never heard of the siv thing though, Any gaeilge speaker I’ve spoken to always said sav or sa to me.
*disclaimer, I don’t speak Irish btw(bar a couple of welcomes etc), though I do wish it was something my grandparents passed down, got lost at my fathers generation though.