This is what I mean: even when you explicitly state no interest in Brooks, 2 out of 3 (rule of thumb) advices will be to use Brooks anyway.

Breaking with my original promise, a precondition for a comfortable plastic saddle is that it needs to be decently profiled, in any projection you look at it. If the saddle looks like a piece of log in some projection, it presumably feels like that when you sit on it.

Surprisingly you can find comfortable saddles around the lowest price bin. My favorite has been a steel sprung touring saddle sold under a variety of names, Avenir, Velo and Endzone with adjectives Plus/Plush and Comfort, which you could have for as little as $16. I am sure you can find a descendant of that saddle, unfortunately with some elastomer suspension now. Look along the line of Velo Plus Comfort. Otherwise check saddles offered as touring but for those comfort usually combines with substantial weight. On the lighter side Selle SMP TRK is very good. I'd go for a woman version, irrespectively of your gender.

For rain riding, spraying the saddle with a water repellent such as for shoes will help. Surprisingly, even a cloth covered saddle will work then.