The Gen 4 glocks have a magazine release that can be swapped to the Right side. This takes care of almost all issues a Leftie has with a Glock.
That leaves the slide release lever. Most solve this issue when doing a Slide Lock Reload by just doing a Reach Over and pull the slide back to release the slide.
I would not hold my breath waiting on the ambi slide release lever on a 45. It will probably come, but that could be down the road.
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SLIDE LOCK RELOAD
ONE: Slam in a Magazine
TWO: Reach Over to grab the back of the slide and pull it back a Hair to Release
THREE: Release the slide when it stops moving back and Let the Slide slam forward chambering a round
FOUR: Reacquiring the grip with your support hand
The Right side magazine release button is really the only thing you need on a Glock. With a Gen4 it can be swapped to Right Side Operation in a matter of minutes without a Gunsmith. You Tube is your Friend here.
Be sure and check out the SF Glock Models. They should have a more manageable grip size, unless you have big hands.
If the G21SF grip is still too big for you, you have one more option with a Glock. Check out a Gen 4 G37. You can relocate the Magazine Button to the Right Side, and it has a G19/23/32 Grip size, making it very shootable. It is chambered in 45GAP which is not a big problem if you order your ammo.
Bob R