Another vote for the Ithaca M37 Featherlight. It's what I learned to shoot shotgun with. Very reliable, well made.
I recently sold 3 M37’s. (2) 12ga featherlites and (1) 20ga featherlite. The 20ga was a hard one to give up but I’ve still got another in the safe.I don’t know if it’s the lightest..but I had an old Ithaca 37 featherlight that was very lightweight (i think it came in right at 7lbs loaded), had wonderful balance, and pointed lightning fast…
I let a friend have it a few years ago… he really wanted it and has quite the collection of Ithaca’s… I’ve regretted it ever since…