I am much taller and bigger than you! Ironic, being Japanese I am 5'10" with my taller and bigger frame, it's probably different. But I think with practice you could handle 9mm. I have a Walther PPQ as my every day carry arm. That's what I use and it works for me. At your size. Try .380 and work from them. I'm more than confident you could handle it. Look at Ruger's .380's they're not bad and not as expensive as the Mustang. The Mustang has had pretty iffy, if not bad reviews. It's not accurate and for it's 650 dollar price point. You could do much better. I'd also look into Walther's small frame revamped PPS.