I FOUND AN ABANDONED MINESHAFT!
Coordinates to entrance of cave leading to it:
X: 274, Y: 65, Z: 340
Follow the cave around the right bend, and you will quickly come to an opening that goes super fast down. I poured a bucket of water at exactly:
X: 267, Y: 49, Z: 327
Using the water as a kind of elevator, you can go either all the way down, or you can get off at the abandoned mineshaft.
Actual abandoned mineshaft coordinates:
X: 269, Y: 33, Z: 326
(Obviously that's just one point in the mineshaft)
I haven't explored it at all; the moment I found it I grabbed my cellphone and came on here to let you know!
This is really weird, because this is the nicest flower forest I've ever seen.
It is far right side, exactly in the middle.
Coordinates: X: 383, Y: 75, Z: -13
It has TONS of allium, every color tulip, azure bluet, as well as rose bushes, peonies, and lilacs.
Now I'll be honest, I don't know how "flower forest" is defined as a biome, but the vast amount of flowers is incredible. I do not understand why it would not appear for you, especially since you've tried recreating the world.