Flatwound preference?
 

I'm wondering what kind of flatwound string to buy if I want that really fat Jimmy Haslip/Mike Pope-esque sound. I'm going to be buying a Warwick corvette fretless 4 string, so any help would be appreciated. Thanks!

I use D'Addario chromes, ECB82's on a Squier P and a Squier P/J special. Love that tone...

TI r sadowskys..love them

Chromes are good. They have a very particular sound (A good one, put it isn't Ideal for everything).
TI's seem a great all round string but can be pricey. Supposed to be super for fretless, I like them on a fretted bass.
For super traditional flats try GHS precision flats or La Bella Deep Talkin' flats. Mountains of thump.

Fender 9050CL steel flats in 45-60-80-105 have a great, fat, almost growly tone to them that doesn't "thud out" over time. Inexpensive, consistent both string-to-string and up the neck, can mellow when you want the to and grind when you want them to. They are the least known but most versatile flats out there. I still have on the set I put on two years ago, and I play everything from Thursday night to Sunday morning with them.

Roto 77s are great
I believe they were the strings Roger Waters used on Dark Side of the Moon

on my Lakland HB Sadowsky flats sound amazing

Roto 77's are great . . . very taut and bright for a day or two . . . then they become very mellow with great mids and lows. Only issue is they're low output strings. I had EAD as Roto 77's and G was a chrome (when I was swapping strings) and the chrome was almost twice as loud as the 77. They have to be tried to know if that will be an issue (It might be with low output pickups).

I will try the 40 - 100 set of 77's next, as the 45 - 105 set I tried was extremely high tension.

++1 for the fender 9050. A rich/full sounding fundamental, not just the percussive thump. I never thought I'd stick with flats on my fretted jazz until I put these on. I was a DR sunbeam guy (D'addario nickels before that). As iiipopes stated they are truly versatile. they'll thump some and get growly when you dig in. The top end is very nice for flats and responds well to right hand dynamics (better than chromes IMO).I use light gauge and love em.
also to my surprise I've kept GHS pressure wounds on my fretless jazz (ebony) though I'm not after the traditional type barky fretless sound. Nice deep smooth bottom end that really shines at low volumes. more like a big cats PRRRRRRRRRRR..
it all comes down to what you are after and when you get the ones that "just fit" you'll know right away. good luck with your search.

I use a bunch of different ones.

GHS Brites on my Applause acoustic/electric.
GHS Precision on my Hagstrom.
La Bella Beatle Bass on my Hofner.
GHS on my Ovation 6 string.
On my Epiphone Dot I think it's Dean Markley, but maybe not. My local store only had one set of 6 string flats and I had them installed during set up.

ILike GHS Stainless Steel precision flats on my USA G&L L2000 45-105 Nice warm / dark tone. and they don't break the bank. I tried the chromes abit bright for me but a very nice string.

Another approval for the Fender flats. I love 'em. I have a set on my fretless, I can get a nice uprightish sound when I roll back the bridge pickup, but it can also sound like a burping duck when I solo the bridge. I also have them on my P. Kinda like the Roto harris for half the price. almost.

GHS absolutely.

Right now, I am loving DR Legend flats. Thy sound great on my SB-1. Used them in the studio for a rehearsal today and was just astounded.
They're a lot like LaBellas, I think.