24" is a good size although you could go narrower if you are a thin person......

Good question timmehall. The International Code Council states the minimum width for shower access and egress
openings (clear and unobstructed finish width) be no less than 22".

We have, on occasion, installed 24" openings just as Lampert Dias suggested, though recommend not going smaller than this. In fact, our preferred standard at Revive is 28".

Hope this helps!