I submit that we can count on one hand the number of films that have only one sequel after which the producers, directors, main actors etc. decide to leave well enough alone and then stop there.
To clarify, I’m talking about a quality film that can stand on its own merit, that didn’t seem to be a lead-in for a sequel or part of a long-running series. Then with the success of that feature, the principals get together for another run and make a follow-up that is as good as the first. And finally, the filmmakers show remarkable restraint and don’t go any further.
To that end I propose that there is only one successful accomplishment with these criteria and that I will wager the following: I will spoiler box my offering and ask that the first ten responders -assuming we can get ten- to not view the contents. I am certain that amongst those 10 respondents, at least 8 will be the same as my spoiler boxed film and if not - I will eat a bug.
I was going to say The Three Musketeers and The Four Musketeers. But looking at IMDB shows that Lester went back fifteen years later and made The Return of the Musketeers. I hadn’t heard of this before but they added C. Thomas Howell and Kim Cattrall to the original cast so I have strong doubts.
Another reason the first two might not meet the OP’s criteria is that they were made as a single production and released separately. Not a case where, as the OP stated, “with the success of that feature, the principals get together for another run and make a follow-up that is as good as the first.”