Sorry I'm not gonna tell you what you want to hear.
But the Ruger LCP in .380 is a excellent back up gun and very easy to carry in ankle holster or a pocket holster.
I carry mine in my front pocket in a DeSantis Nemesis holster ( I never know it's there.)
Years ago when I was a LEO officer I carried a S&W compact 9mm as a backup.
Man it was a load - I mean a load to carry.
I'm not aware of any 9 mm that are as light as the LCP
So you got some decisions to make - weight vs. caliber.
Good luck with your decision.
Let us know what you decide.