@Sarah62 My trainer was a gymnast in a previous life, but does rehabilitation now as well as general personal training. I booked in to see him as part of my weight loss, but I mentioned my stomach and he asked a few questions and then he said "we can fix that". I was pretty shocked as I thought it was something that I'd just have to live with.
We started slow, he showed me how to do a proper sit up, not needing to go up all the way. We focused on the core and my back, as he said that the back need to be strong to support the front recovery.
It's hard to explain, but most of my exercises focus on "fixing" my position on the floor. If you tie a resistance band onto a chair logout it across the floor and lie on it so it is at the small of your back, pull it tight, then tilt your pelvis so that your back traps the band, that's the position I do most of my exercises in.
I started this with small sit ups, legs bent and position "fixed", keeping the band tight and trapped.
I don't count reps either, as he said that's the quickest way to loose motivation, I use a tabata timer app and focus on good technique instead.
I owe him everything, he has changed my life. I'm more confident, loosing weight and I can suck in my tummy so that under gym tights it looks semi flat!
Yesterday I went to a tabata class and was able to roll onto my back from sitting and back up to a sitting position with my arms above my head. 6 weeks ago, I couldn't play football with my kids because it was so uncomfortable.
If you want to PM me I can try and find a way of showing you my exercises.
Good luck! You've got this!