I set the key left to the spacebar (usually Alt or Cmd) to act as Ctrl in Emacs, so I can press it with my left thumb. This can be done in the Emacs config like this
(setq mac-control-modifier 'command)
(setq mac-command-modifier 'control)
(setq mac-option-modifier 'meta)
(setq mac-control-modifier 'super)