Any period costume is going to have a corset: if you put someone into a costume without a corset, it won't even do up. Corsets do reshape the body, and a leading actress will have her corset made for her. There are plates and engravings which show women being measured for corsets by men in the 1700s. They were made of whalebone, and sometimes metal, and fabric - probably linen - cut into certain shapes. There would be rows and rows of stitching, and you'd tuck the bones down. I've seen a 1720s corset which had an iron band in a curve right round the top, and straw padding. I wouldn't do that to someone.
In the time of Tom Jones, the bust would slip down inside. It's like wearing a very tight dress without a bra; it's a flat front, a triangular shape. You can't wear a bra under a corset: it would be really uncomfy. Instead, you wear a chemise of fine linen or cotton, with a boned petticoat. Anyone who has done period drama is used to corsets, but it's a bit of a shock the first time. Actresses get quite obsessive about it - they say, "Is it meeting at the back?" They get addicted to it being pulled in right.Reuse content