Tips on going gray gradually?

I have been coloring my hair for 10 years. I use Perfect 10 Light Brown and love it, but I am 47 and feel it is almost time to start letting it go naturally gray. I want the process to be gradual so the white roots situation is not shocking and painful to look at. Should I use the next lighter shade of Perfect 10 or should I switch to a semi-permanent dye instead? Should I get my hair professionally lightened? I have very long hair and want to keep it long. Any tips and suggestions would be very appreciated.