I'm a Lefty. Always have been.
Glocks and Sigs are not really lefty-hostile at all, even if you don't take advantage of Sig's ability to reverse the mag release.
I would humbly and respectfully suggest that if you're having problems with those guns, that you're not using the correct reloading technique to begin with, and learning to effectively reload guns as neutral as those will serve you better than getting a different gun. (Of course, if you simply *want* a different gun, that's fine, but should be motivated by other reasons.)
Teaching this technique is difficult in text, and honestly beyond the scope of what can be properly transmitted online. For reference though, here are the factors:
Mag release: This is effected with the 2nd knuckle of the trigger finger of the left hand. Essentially, you curl it up and press it against the mag release. If you need additional pressure, you supply it by pressing the frame of the gun towards your trigger finger with your support hand. With practice, you will not need your support hand to drop the mag.
Mag insertion: Very hard to describe in text. The fresh mag should be grasped such that the index finger of the support hand is touching the nose of the topmost cartridge. The hands are brought together with a "pointing at the pinky of your gun hand" motion, which gets the head of the mag into the well of the gun. As the motion is continued, slamming the mag home (hard!) the fingers splay out, such that the heel of the palm drives the mag home.
Slide release: I belong to the school that says that no one should use it. To be more precise, I belong to the school that says that the only people who should use the slide release are those who a) happen to have correctly sized and positioned hands and fingers to easily reach the control (which eliminates all Lefties and more than half of Righties) and who can reliably, 100% of the time engage in acts of fine motor control fully equal to their gross motor control when under life threatening pressure. (Which eliminates anyone who meets the previous criteria.)
The technique in this light is, the heel of your palm still being in contact with the mag you've slammed home, you pivot your hand around such that your fingers can wrap over the top rear of the slide, which you then grasp firmly via wrap over. Your gun, still being pointed generally at the target all throughout the reload, remains so. You then pull you slide grasping hand towards your gun holding hand's shoulder, releasing the slide at the end of it's travel. Your slide hand continues its journey to the shoulder, lightly touching it.
This technique provides right and left handed shooters with a reliable technique that works on all guns, even under pressure. Using it, the left handed shooter can reload as fast (or faster) as any right handed shooter using any other technique.
