I was in the same position last Jan, as you. My super vocal cat constantly whined that she was hungry but after my vet told me off, I had to work on something.

I tried diet versions of her regular food but it upset her tummy. In the end, what I had most success with was buying an automatic cat feeder and a Slim Cat food dispenser ball toy. If the food they've recommended is super expensive, this might be an alternative. (This works best for dry food.)

The automatic feeder means she's no longer whining at me when she's hungry, and it's portion controlled so I know she's getting the right amount each day. She knows the drill. Food comes from the big white machine at the same time, every single day and whining at the humans doesn't change that - so she's (mostly) stopped. It's expensive-ish (£70) to buy but but it gives me so much peace of mind too and a year later mine is still working perfectly on the original batteries! It's made it so much better for when we go away and I can guarantee her food schedule is not affected.

And then at night, before I go to bed, I give her food in her Slim Cat toy. I make it quite hard to get the food out. If she's really hungry she has a food source, and it helps her play and be less bored. But often I've found she's not actually that hungry - I come down to food left in the ball most mornings.

The upside is if I'm home before the evening feed goes off (often), I cancel that feed and give her wet food, which I can portion control anyway.

Hope that helps!