The best pork for making sausage isn’t the standard ground pork you can buy in grocery stores, since that’s too lean. You want to use pork that’s approximately 80:20 meat to fat ratio and I find that boneless country style pork ribs are a great, inexpensive purchase with a good amount of fat.
Despite the name, boneless country style pork ribs aren’t ribs at all. They’re nicely marbled, rib shaped strips of pork cut from the shoulder. I usually grind my own at home, since Mr Meatified brought home a meat grinder a few years back, but you can ask your grocery store butcher counter to grind the meat for you.