Some folks have suggested that you need to start your search by finding a pistol that fits you, and that is comfortable. Great suggestion. I'm amazed at the number of people who buy a pistol before they have actually held one.
We are finally beginning to see small 9mm pistols coming to market (about time); and some of them look good. Of course, there is a wide price range. Kimber Solo is kinda pricy and Kahr new CM 9 is much less. Beretta has announced a new small 9 due out in October. AMT has had a Backup 9 for a while. If money is not object there is Rohrbaugh (sp?). Springfiled's EMP is quite an investment, too.
My point is do some homework, pick a price range, and hit the shops. You have a good crop to pick from and you'll know it when you have it in your hand.
I've found that I prefer carrying a revolver instead of an auto-loader. It's simple, lighter, and smaller than most compact pistols. The Sub-compacts are no where close to comfortable for me either.
I must be weird or lucky. I got a mini-tuck for my PT709 and found my double stack .45 (!) fits it fine. The grip is of course thicker, but it still disappears on me, and the weight bothers me not at all (it's not plastic).
I've felt comfortable with a compact double stack. With the right holster concealing isn't an issue. I do like the single stack 9mm carry options in theory but I find that I don't train enough with them to feel comfortable carrying one. If you can put in the training a PF9, PM9 and Ruger are good options.
The gun I carry on the outside of my winter Carharts is not the same gun I carry at the beach in shorts and a T-shirt while training my dog.
You will need 3 EDC guns if you really want to EDC.
I have a small pocket .380, a compact 9mm and a big .45 that are dedicated to EDC. The 9mm is the workhorse and is a double stack. The .380 and mace are next then the .45.
I'm small, 5' 3'' on a good day and 124 lbs. I find the Kahr PM9 to be just right for me. Mine is equipped with the Crimson Trace laser guard. Anything larger is hard to conceal on my body, and I can manage the recoil and prefer not to go .380.
I have an XD9 subcompact and I love it. I like the size of the subcompact frame as well as the little things that make it an XD (like the loaded chamber indicator and the grip safety).
Before you buy an EDC pistol I would recommend taking a serious look at how and when you will carry it. Do you need it to be easily concealed, or is it ok if it's seen? Are you comfortable with a smaller round or would you like to stick with 9mm? Try out as many different pistols as you can and pick one that is comfortable to shoot and carry. It doesn't matter if it's single stack vs double stack or whatever as long as you're comfortable with it!
I have heard good things about khars but unfortunately have no first hand experience with them. Since you say you like your xd9 I would say check out the xd9sc first before anything else and see if it feels as good to you as your xd9.