This and this are great posts on Medieval Silkwork that are some of the most in depth articles I have seen.
By My Measure also has this article about the breast mounds and cleavage visible in art. And her own example.
This web site has the most in depth images of Austrian Tyrol finds.- It is in German I believe- but the pictures speak for them selves.
This pinterest board of mine has some of the artwork in this post, along with others recreations and research. Check it out.
After all the info I have gathered I decided to make my own supportive garment. My biggest reason is because my weight can fluctuate massively from one day to the next. So I can make my other kirtles and surcotes more skimming and still have them fit on my bad days, without them gaping.
The fabric I used was med/light weight of a Linen/Rayon blend, but otherwise hand sewn including lots of eyelets.
Here you can see the spiral lacing. I had to modify it after I had made it, because the fabric was too high into the arm pit and was chafing badly. So I lost the top couple of eyelets. Hence the unused eyelet near the top to create the spiral lacing. I only laced it on one side.
This is THE MOST COMFORTABLE thing to wear! I am a B cup, with a fairly high bust to start with, so I just need gentle shaping. But this could easily be supportive for a larger bust.
The front seam is curved, without any breast bags, or cups. The bodice was cut strait for about 9" under the bust line, which has been folded up to create three layered band of about three inches long, leaving only a single layer on over the bust. If you are bustier or want a warmer garment I would recommend more than one layer. As is this will be great at keeping my bust cool!
The lacing strips are 4 layers thick with eyelets every 3/4" Above the band the lacing can be let out or tightened depending on the look required for the garment, and the fluctuating size of my bust. The lacing at the band is kept tighter, so the garment doesn't shift.
The skirt is pleated and sewn onto the bottom of the band. The skirt keeps the band from flipping or bunching when doing actual things.