Mooh, I didn't know you was a bass person. Ever neat!

Banjoman, before you jump straight to flatwounds (flatwounds on a P-bass will give you that 'thunky' sort of sound characteristic of 50's rock 'n' roll), you should know that there is a medium step you might consider. There is a type of string known as a groundround. It maintains much of the fullness of a roundwound but plays much more smoothly, and you'd lose that "scratchiness" you're talking about.

There are various brands: GHS Pressurewound, Rotosound Compressors, etc. I preder D'Addario Half-Rounds on my fretted bass (and LaBella Black Nylon Tapewounds on my fretless)

The question is asked, "Do bass guitar strings take a while to play-in?" Well, I do know that Ralph Schipper, Fred Eaglesmith's bassist for many years, used to use stainless steel wound (i.e. usually for electric bass) strings on his Guild B-40 acoustic bass guitar. He told me that he never felt he had the right sound until they'd been on for 2 years!