Whilst my sisters and mum are by no means large, they are addicted to the shopping channel on pay tv. (tvsn) . They recently bought what is called 'bella bodies shapewear'. A bodysuit that compresses and flattens the tummy and midriff areas while still feeling sexy and comfortable!
It is like an instant tummy tuck and can reduce up to 6cms depending on your size and its made from 4 layers of microfibre ; it provides seamless support with no messy zippers or boning.....it cost them $64.50 plus P+H.
My sister, who has had 2 children, is 28 years old is prob a sz 12. Not fat at all, just needed toning etc. I saw her last weekend and she had this bella bodies on AND her tummy was so flat. She was wearing a sz 8 tshirt. SHe looked fantatstic !! It didnt make her look necessarily slimmer, it just made her look toned and flat - IUKWIM.
Maybe worth taking a look, they have a 30 day money back guarantee no ?'s asked....
good luck.