I have the Flapjax, which are 100% cotton, so I took them in a 27 (my regular non-stretch size). Although I can fit into a 26, b/c they're so low, they sit right on the top of my hip-bone & were too snug when I sat down & . They stretched a little & since I've lost weight from my initial purchase, it was a little looser in the seat.
You might want to try either the Flapjax or Rodeo b/c they're the same cut. However, I haven't tried the Western Cinema which has 1% stretch & a yoke in the back. I imagine I'd take a 26 in those, but need to try them on just in case.
LMK if you need more help. There's a boutique a mile from my home & I can ask them if they're getting in the Western Cinema.