On my MacBook I map the right hand command key to “ctrl” and the right hand option key to “meta”. Since the command keys are right next to the space bar that puts the ctrl key on a thumb position most of the time, and for the times when that isn’t a good key for a given combo I still have caps lock bound to “ctrl” as well. Seems to work reasonably well and lets me keep the usual command and option keys on the left side for “super” modifiers and for typing accented and other characters.

For my desktops, I use an Ergodox EZ keyboard and mapped ctrl and meta into the thumb clusters there.