@Vezelay and others with the "flat bum" issue:
I kept trying all of the "alterations" recommended with no success and decided to try one more method before resorting to drafting it all myself.
In my youth, my bum was a wee bit too large, tiny waist, and "the girls" were generous in size. Shoulder pads of the day balanced my narrow shoulders, so I worked the Marilyn look with what I've been informed was "success".
Always expected to grow a massive huge bum if I gained weight with old age - not so! I say "Hello" to my Gramma and laugh anytime I see my naked body in a mirror- Massive "girls", NO waist, and a very flat bum-, 6" smaller than my chest.
However, after closely studying numerous selfies of my back side, I realized, my bum isn't smaller - all of the excess volume now hangs down underneath where it used to be - just like "the girls" these days. But propping up with underwires there would be painful!
So I took a pants pattern and scooped out the bottom of the back rise so that it looks more like a "U" instead of "J" . Basically, my bum is lower than my crotch point. I also added some length at the top. In order to taper the legs (my fabric was woven, not knit) I had to lean the back of the "J" outward- like a jeans' pattern. Not certain that would be necessary with a 2-way stretch knit.
So if the "flat bum" is age related, gravity has parked the excess "junk in the trunk" underneath the trunk - and ya gotta make room!
Hope this helps, and sorry I still can't do pics.