I am not left handed but when I went through the NRA LEO Instructors course Mas Ayoob challenged me to shoot all the exercises and qualifications weak hand only. I did so and had the second highest score.
I used a P7M8, it is the best ambi handgun made in recent times and probably the best left hand gun. The only external control really is the mag release and it is available on both sides. To release the slide after a reload simply squeeze the squeeze cocker and the slide is released and the gun ready to fire. Not going to shoot after the reload? Simply relax your grip.
I too shoot using either hand. I like to play with my Beretta 92FS with either and, as well as my constant companion Kahr PM9.
Interesting thing about left hand shooting is when I took out my Beretta PX4 Storm. Being that it uses a rotating barrel, when shooting right handed it torques nicely into my hand, but when shooting left handed it feels like it wants to torque out of my hand, a very uncomfortable feeling. It is the only pistol that I have that I only shoot right handed.
When you're left handed, you learn to adapt pretty quick. Our duty weapons were Sig P226's. I could work the mag release and decock lever with my trigger finger. Just grab the slide with your right hand, pull back and release. I pretty much prefer Glocks now. Work them the same, but don't have to worry about a decocker.
I shoot pistols lefthanded but shoot longarms righthanded (who knows?). Anyway, Glocks have been great for me, few controls to master, and using the index finger to hit the mag release becomes second nature with a minimum of shooting.