Again, thanks for the replies, everyone.
I stopped by the local GC yesterday, and picked up a set of Dunlop nickels, just to try them out. Given what John Wentzien and others here say about them, I figured they might be close to what I'm looking for. And they were cheap! (always a plus...).
So far, I'm impressed with them. They're still new, and so they're a little bright, but nowhere near as much so as the Rotos were on that bass. I think they'll mellow down into just what I'm looking for.
I'm still drawn to the idea of the GHS Pressure Wounds; I'll probably try a set of those on my fretless.