I have a Domane too. Same experience as you with the stock saddle. It's not BAD, but on a rougher road and with less thick chamois pads, it's no good for more than 20 miles.

I tried a WTB Volt saddle; no better than the stock Trek or Bontrager saddle.

I can't see the C17 getting any softer.

The one I ended up with on my Domane is the Selle Anatomica X-2. It's kind of in the Brooks leather style, but with a big perineal (prostate) cutout and with a leather preparation method that makes it softer from the beginning than Brooks. We adjust the softness by adjusting tension with a bolt under the nose. It's like a hammock. I like mine nice & soft, so my under parts are suspended just above the top of my seat post. I find the leather treatments they sell are not needed. The skin oil and sweat soak into the leather and form a waterproof oil finish in time. Just try to avoid it getting rained on until that happens. (just a few really sweaty rides is all it takes, hehehe)

I have a Selle Anatomica X on my gravel bike. It's not quite as good as the X-2, but better than Brooks.

I have a Brooks B67 (like a B17, but with rear springs) on my 20" wheeled folding bike. It's 10 years old with a lot of miles on it, but still harder than either Selle. It does help with the bumps in the road, though. I miss the cutout. I tried to sell it, but can't get a decent buck for it, so I guess I'm stuck with it for life, hehehe.

Here's a good shot of the B67 on my Tern Vektron. I give it an 8.



Not a good top view, so you can't see the cut-out, but here's my Selle Anatomica X-2 on my Domane. 10. I'll post again if I find a good top shot. It was more of a honey color when new, now it's more medium brown. I ride 40-50 miles with no pain and after a century, I'm just a little sore the next day.