I created my own one hand layout since I have the Kinesis keyboard where the keys are split. So something like Dvorak one hand would not work for me. Also note that I remap using Autohotkey which allows very sophisticated key combinations and locking. This allows me to shift lock without holding down the finger, especially since it's the pinky finger which would cause a lot of strain on it. Also since it's an Autohotkey script, I run it only when I need it.

So I'm using exactly one half of the keyboard because the keys are split and the other half is too far away to reach. Each half of the normal letter keys are 5 wide by 3 rows, or 15 keys. Double that is 30, which is more than the 26 letters in the English alphabet. So we divide the letters by frequency such that more common letters can typed normally, and uncommon letters need a switch. So we need a trigger to switch between these modes. I use scroll lock and reprogrammed one of the pinky keys to toggle the scroll lock. So the script checks whether scroll lock is on or off when you type a letter to know which letter to send. That is, scroll lock is reprogrammed to switch between the common and uncommon letter modes. Now uppercase letters is handled by caps lock, naturally. Caps lock also acts like Shift in the case of punctuations. However it's not that simple. The script must know the state of both the scroll lock and the caps lock at all times. Both locks are turned off after a letter is typed. That is, it returns to the common unshifted mode after every keypress.

I type with the right hand, so the layout looks something like this (it's actually 6x3 counting the keys to the right of the pinky):

Common mode unshifted:
fhtrc,
uieoa[CAPS LOCK]
dnsgl[SCROLL LOCK]

Common mode shifted:
FHTRC.
UIEOA
DNSGL

Uncommon mode unshifted:
'zyq<[
jmwpb
"vkx-

Uncommon mode shifted:
;ZYQ>]
JMWPB
:VKX_

You may have noticed that my layout is surprisingly similar to Dvorak. So Dvorak users should have an easy time with it. The common side is pretty great. It's easy to remember, since all the vowels are on one row like Dvorak, and you don't need to shift very often because the 15 common letters comprise 80%(?) of most texts. however, you may need a cheat sheet to remember the uncommon keys.

A major issue is you may overuse the pinky to shift modes. if you have a foot switch, it would eliminate this problem.

i'm not sure exactly how you use the mirrored layout. you use a special key or foot switch to reverse the mirror? in my layout, the common letters are typable without switching modes, reaching, or any other manipulation.