I have an XDm 4.5 in .45 ACP. I'm not a big fan of the XD sub-compacts because the barrels are too short to provide what I want in ballistics. On the other hand, my shooting partner recently bought an XDm 3.8 Compact in 9mm. You can carry it with the short mag. and carry the full size 19 round mag. and appropriate extension for back-up, or to make it feel more like shooting a full size 9mm service pistol at the range. If you're not going to carry it, I'd recommend an XDm over the XD because the barrel and sight radius are .5" longer and the XDm's barrel is Match Grade and with the interchangeable backstraps, you can use the one that makes the pistol feel best in YOUR hand. But that is also true for the 3.8 Compact if you want to carry it. For anything thinner, you might want to look at the Ruger SR9 or SR9c. If you want something thinner and smaller, look at a S&W Shield or wait for the XDs in 9mm that will be released to the market very soon.