I think you are overly limiting yourself. The size difference between the .25 and the Glock Model 26 is enormous.
I'm not a fan of the .25 for self defense. It just doesn't penetrate deeply enough or cause enough tissue damage to reliably stop an attacker.
Personally, the smallest I'd go is .380 ACP for a "deep concealment" gun. There are so many .380 choices today that are only a little larger than your .25 that I think it's in your best interest to at least consider them if you really need a deep concealment gun. I mean, if you have to have a deep concealment gun, why not have one that is much more effective than a .25?
But, if the choice is JUST between your .25 and the Glock 26, I'd say go with the Glock. I'm just not convinced of the actual usefullnes of the .25 if you ever have to actually shoot it at a bad guy.
Trebor knows his shit (I've trained with him), and I'm glad to hear him say this, because it's exactly what I was going to say.
The .25 isn't a reliably, immediately lethal round. Now I know, about twenty chuckleheads in the back of the room are going to start saying, "Ok, then, can I shoot you with one? Hyuck, hyuck, hyuck." No, you fucking moron. I'm not volunteering to let you stick me with a sewing needle, but that doesn't make it a good choice for self defense. Shoot me with a .25 and I may bleed out...but I can probably get this bent steak knife into your wife's guts before I do, EVEN WITH PROPER SHOT PLACEMENT. That makes it a no-go for me.
So basically I advocate any plan that involves never relying on the .25 as a defensive round.
Steph's got a Beretta .25 that her grandpa gave her. We pop off a few at the range from time to time, but neither of us would ever carry it. It is a cute little thing, though.