The part that sounds like you need is called a "freehub body". It's about a $30.00 part. Removal usually takes a 10mm Allen key. They come in 7-speed and 8+speed versions so, if you have a 7-speed now, it will simplify your life to replace it with the same. I've replaced a bunch of them but none for probably a decade. I never paid any attention to the group set the replacement came from and they all fit and worked.
__________________
My greatest fear is all of my kids standing around my coffin and talking about "how sensible" dad was.