Chicken sausage is fun to make, and we’ve done quite a bit of it here in our test kitchen. You can definitely add the skin to help increase the fat content, and adding pork fat is always an option as well if you don’t want a 100% chicken sausage. Thigh meat is fattier than white meat, so that helps as well either doing all dark meat, or part of both.
We’ve done chicken sausage as 100% chicken breasts, thus probably 95-99% lean, and used chicken thigh meat to make 88-92% lean.
Probably the best version we’ve made here was with 100% thigh meat.
Adding water and a meat binder like Sure Gel will help with a lean sausage like chicken. It’s hard to exactly say how much to use though, and how much water to add. Chicken will purge a lot during thawing, and even chicken that is already “water added” or pumped may slightly vary depending on how well the already added water bound to the meat already. We’ve typically varied the amount of added water and Sure Gel each time. Adding some will be good, but if you do too much, it will make the meat really soupy since chicken doesn’t have the same structure to it like pork or beef. It will also really help in making chicken sausage if you keep the meat extra cold to give it a little extra structure and not get too warm and start getting soupy.
Let me know if I can help with anything further!