You're using a C41 B&W film which will not give you a look that true B&W films are capable of. For the brightest whites and deepest blacks, switch to a true B&W film (Tri-X is an excellent place to start as it is very friendly to less than ideal exposure and development), and develop in D76, which is also very flexible to use. You don't need to nail the development in order to get great negs. The two were essentially designed to go together. Even easier, develop the Tri-X in Daiafine, a very simple to use developer that as far as I know is immune to over development. Put the film in it for the recommended time and after that it won't keep developing.
It may seem daunting at first "rolling your own", but it isn't, and the necessary equipment you'll need like the developing tank and change bag are inexpensive, and a one time expense. Kodak Rapid Fixer can last a year or more if stored and used properly, vinegar can be used as a stop bath, and once you buy your developer it can be mixed into a stock solution that can be used for many rolls of film. Measuring gradiants can be simple liquid measuring stuff from Walmart or a thrift store, and you can safely keep your chemicals in washed out soda bottles for quite a long time. There are better bottles available, but the soda bottles will work fine if you top them off and put some Saran Wrap on the top under the cap. Get yourself a cheap glass thermometer and you're done except for some distilled water from the grocery store (or you can boil your tap water and let it cool down), Buy some Photo-Flo to avoid drying stains on your negs and you're done. D76 can go "off" rather quickly, so I would start w/ Diafine or use TD-16 from Photographers' Formulary, a D76 clone that will keep much longer. It's more money than the D76 though, so perhaps the Diafine is a better way to start rather than D76 now that I think about it. Whatever you use, it will cost you a LOT less money than sending your stuff out for developing.
You have a camera and lens (I assume you have the usual 50mm Pentax lens on the camera) that are capable of giving outstanding results. I keep going back to the shots that I took w/ the very same setup when I first started getting serious about photography eons ago, and those shots still look really good. You may as well give give yourself something that will be in line w/ the same quality of your gear. Not that there is anything inherently wrong with XP2, but being a C41 film it's more difficult to learn to process at home vs traditional B&W films, and in looks and tonality it sure ain't Tri-X. Don't forget that flat negs are often the result of flat lighting or underexposure too, so that needs to be right no matter what you shoot. Once you get your equipment and chemicals together, ask questions here and we'll help you out. I have a lot of the gear you would need to start developing your own stuff that I could sell you for great prices, as I'm transitioning (again) to painting. Later, you can learn to obsess over different developers and films and argue their merits endlessly here :}