You don't state if you will be using the new 9mm as a CC or not. Your current set includes a full-size 9 and 40 with mid-sized 45 capable of range duty or CC if you are able to where you live.
If CC is a possibility, then I vote for a Glock 26 as well. It would be a good bit smaller than the 3.8 and still comfortable as a range toy (and to get further CC trigger time). It looks like you live in NY so capacity may not be possible. More options for CC are the slim guns. Shield, XDS (9 or 45), or a Walther PPS. All are great choices depending on how it feels in your hands.
If CC is not on the table, then a G19 would be nice. A 19 will conceal quite well but isn't that much smaller than the 3.8. It would be a nice addition to your current set.
One last thought is something you didn't ask about. A 357/38 revolver. Perhaps an SP101 in 3". Really comfortable and super fun at the range. Also, if those crazy politicians in your state go further off the deep end and ban all semi-automatics; you'll have a viable CC option. The SP is a little chunky but still capable of CC where high cap mags are not allowed. That heft makes it really fun to put rounds downrange. A wide variety of options is a good thing in a crazy political environment.
Good luck in your hunt.