Regarding the "settling in" process, with both bass and guitar
I've found that a great deal depends on how you wind it on the post.
I can minimize the "stretch" by using the "first-wind knot" method.
(OK, I don't know what it's really called but I'm sure there are
a bunch of youtube demos of it.)

I too have been playing bass for a long time.
I have flat wounds on my 1976 Fender Precision and I keep them clean.
I've only changed them once, and I like the sound I'm getting.

LLOYD S