Spanx - I swear by them - if you have a large shopping centre near you you may be able to find the Spanx All the Way High Waisted Briefhose (have a look at them on Figleaves.co.uk) - because they go up to the bra line they hold everything in, and also smooth your thighs. Plus, because they're tights, you don't get the seam digging into the thigh that you do with the bodysuit versions. Size D fit me, I'm a size 18 trousers and 16 top. They are dear for tights, at about £23 a pair, but I get plenty of wears out of them.
I also use Aristoc Hourglass Toner tights - they give a nice curvy (in the right places) shape but aren't as restrictive as the Spanx, although they also go up to the bra line. I wear the M/L size, and get them from ebay for about £4 a pair, which is a massive saving on anywhere else.
A tip with both of these - pull the "waist" band right up underneath the bottom of your bra and it'll stay put better - if you leave a gap they both have a tendency to roll down a little bit. Oh, and don't be tempted to get a smaller size in the Spanx as they are VERY tight and won't do the trick!
I'm not a big fan of waist cinchers - because they end at the hips I find I get a "hip roll" of fat where it's been pushed down from my tummy. The boned sort bend in odd places and the non-boned ones tend to roll up as well as down.