Taking him to a groomers for a proper all over clip would be away to give you an easier start with the changed coat, then you would be able to attack him yourself every month or so before it gets too thick. Dogs , like toddlers, behave better with professionals. Mine would snarl at me, but submitted happily with a groomer who seemed to hypnotise her clients. You have to ask complete strangers who they take their dogs to, because some are terrible. You could insist on washing and drying him at home the same day so that the appointment is quicker. They want them absolutely clean otherwise any grit and dirt ruins the clipper blades. You will need hairy feet sorting, which is hard yourself!
I bought Andis clippers, very quiet, which is important. I would ask other folks what blade is best for that coat. It’s on our grooming guide section.
Have you tried thinning with a Mars Coat King? Their website advises which blade to use. It would look and feel better, but you need a patient dog, and scissors for bits it can’t do.
We clip my daughters very hairy dog, he feels great afterwards, but obviously it rapidly grows, still thick. He gets matted, and it’s a long job, taking several sessions because he is foot shy.
My thought is that if he is nervous, it may become traumatic for both of you when you new to doing it yourself.