struggling with brush/groom routine

i feel like i have tried so many different brushes, detangler sprays, techniques, etc. pin brush, slicker brush, wide tooth metal comb, and im just not satisfied. i just feel like its pulling so much and i dont want to hurt him. he usually doesn’t have too many mats i just feel like he gets tangled so quickly.

I struggle to get his sensitive areas brushed thoroughly as well like his armpits and around his testicles/thighs which are high matting areas. his wavy hair is just so thick so i try to get as down to the skin as possible but idk maybe im just doing something wrong or dont have the best brand of brush? i feel like i cant get all the way down to the root without pulling or hurting him.

i try to brush him as much as i can and he goes to the groomer every 4-6 weeks for a full groom. i have looked at the chris christensen stuff or whatever it’s called some people say they cant live without it others say its not worth it and it is expensive so im torn. any tips tricks or recommendations of products or techniques for brushing a wavy coat are appreciated!