Be careful when choosing which size to follow, because size numbering has changed dramatically over the past 100 years or so. For example, a size 12 will get smaller and smaller as you travel back in time – today the bust size of a size 12 is 36in, but in the 1960s it would have been 32in, and 30in before that. So, if the pattern includes bust/chest size measurements, focus on these rather than a size. If there’s only a size, try to find the date of publication – fire up the internet again and look for details about the measurements of each size at that time.
The fit of vintage garments was also different. Women of an older era would wear foundation garments like girdles and bras to create a strong hourglass shape. Plus, fabrics were stiffer and the fashion was for tight clothes that fitted the body closely. Nowadays, fabrics are stretchier and clothing tends to have a baggier, more casual fit. This is called ‘ease’ – vintage sizes have less ease than we’re used to, so you might prefer to choose a size larger than you usually would.