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>pinky finger numbness
You're pinching your ulnar nerve. Pic attached shows positions on drop bars, but with flat bars, ulnar nerve pinch is the most common. It's all about your wrist position; padding and gloves won't do shit in this case.
I had exactly the same issue when I tried a bike tour on a flat bar bike: After a few hours, both my pinky and ring finger would start to go numb. It got worse and worse over the week; I bought some bolt-on bar ends midway through the tour in desperation. They helped a little, but my left pinky/ring finger felt a little tingly for almost two weeks afterward.
I switched to drop bars. Being able to shift my hand position around as I ride has pretty much eliminated my hand/wrist pain. Remember, you don't have to mount the bars road-racer low - I place them with the tops about level with my saddle.
If you want to convert your current bike rather than buy a new bike, it'll be a lot simpler to switch to a different flat bar that doing a dropbar conversion - no futzing with compatibility issues between dropbar brifters and whatever derailleurs/brakes are already on your bike.
A swept flat bar like an OnOne Mary or Soma Osprey will allow for a much more natural wrist position, while something like a Jones H-bar or a butterfly bar will allow for multiple hand positions.
