Bryan Woo is the starter I think the Mariners may be willing to part with in a trade for a young bat. The Cardinals would be wise to pursue him.
Woo snuck into MLB's top 100 prospects this year and features multiple fastballs that he uses to strike batters out. At just 23 and only 10 starts into his big league career, he is 1-3 with a 4.96 ERA. Woo was really good in his first few starts, hit a rocky stretch, and turned things around a bit in his last start against Arizona. He's not a ready-made number two or three starter like Gilbert, but the potential is there.
Woo would be under team control through 2029, which is a huge advantage for the Cardinals. Should a deal come to be, I would guess Woo is packaged with one or two prospects to acquire one of Gorman, Donovan, or Nootbaar.