If you have arms, there is a simple device that can be custom made that is very effective at stirring mash. It is called a mash paddle. If you have a gym membership you should be able to work up your endurance to stirring your mash every 10-15 minutes. Slide the paddle to the bottom then raise it back up 4" then stir. You won't disturb the bottom filter layer of the mash.
Every system has an average efficiency. It is effected by many factors. Old grain, different base malts, mash time, and draining your mash tun into your boil kettle which is usually the main culprit. My mash tun drain is 60 min for a PBV of 18 gallons. If I go 45 min my eff % will be off. What ever time you settle on stick with it or your eff% will be all over. If your efficiency is between 70-85 you don't have a problem. It is a number not worth chasing, focus on repeatability of your technique, and not brewing gadgets trying to reinvent the wheel. Most all of us don't brew in a laboratory. Keep it real!