We have rented cars twice while visiting the UK.
I found that renting a GPS with the car was an outrageous charge. My phone didn't work in the UK, so I had to ask for a navigation system on the car.
The nav system worked very well except for two locations, for some reasons. I. had to stop and ask for directions, so no problem.
You are wise to rent an automatic, since if you had to shift gears, you would have to do it with your left hand.
Driving in Britain was not so bad, except for the traffic around London. Brits tend to be polite drivers and not terribly aggressive like some on the continent.
Still, focus on turns at intersections, (stay on the left, my wife kept warning me).