As was stated above, concealment isn't as much an issue as it seems for most people new to carry. I am large-framed and started out with an FEG PA-63 as my primary carry (a Walther PPK clone) and was quite concerned with being able to keep it concealed in an IWB holster. I've since moved on to carrying a Hi-Power an an OWB holster as my every day gun, comparable in size to your HK, except that the HK grip is a bit taller (by about 10mm).
A couple of tips for you to consider:
Barrel length isn't as much of an issue for concealment as it seems to appear for most new folks, especially when carrying IWB. The more critical factors are width and grip size. This is why the 1911 platform is great as a carry option for concealment - it's quite thin even though it is a full-sized handgun.
I think the biggest item of concealment concern for your gun is the grip. The best way I know of to deal with this is to choose a holster with a considerable forward cant. This will allow the grip to be positioned close to your body an minimize the amount of protrusion under your cover garment. High-riding holsters are also a good way to minimize printing, as it puts the gun higher up on the waist and more under the arm where printing is not as likely to happen. I have a high-riding, canted holster (a Galco Combat Master) for my Hi-Power that does the job beautifully. It is easier to find this in an OWB holster, but I have come across high-riding IWB holsters that work this way. Here's a couple pictures to demonstrate how my carry rig looks and conceals.
When you get your holster, don't be afraid to experiment with positioning. It seems that most folks like the 4:00 position. Personally, 3:00-3:30 works well for me, depending on the pants I'm wearing. If you get a holster with an adjustable cant, all the better to find the "sweet spot" for you.