Bike shops have Take-offs, when people buy a bike but don't like the OEM choice of saddle.
See what they have ,maybe ride around a while on it.
comfort is between you and the saddle ,
my butt has its own dialog with the saddle i got.
Its not up to me, its your butt..
I have packing taped thick plastic over my Leather saddle , before , and left it on.
won't benefit from any breathability riding, in my rain gear trousers anyhow.
Now, I have a Fizik Vitesse on one bike a Avocet touring 2 on another
[It's leather covered , so a poly bag goes on it.. ]
lots of nice thinly leather covered saddles, but they won't stretch and sag if saturated
with water, since the nylon base supports the tension..
rather than tensioned leather doing everything..
Besides, plastic bags are not impenetrable.
several of them are.. my favorite saddle cover : the bladder from a 5L wine box.
its a square of 4 layers.. cutting out the valve and slitting a diagonal line
in one side, there is still the edge welded 2 layers on the opposite side..
to keep the 'product' in, it is impermeable..