From what I can glean, Ottoman women wore two items of underclothes: a light underdress known as a gömlek (pron. goomlek), and possibly some form of underpants known as çakshir (pron. chakshir). No one is really sure about the underpants, because no one has ever seen any for women, although they have found men’s. Being the lazy person I am, I chose to forgo making çakshir for my outfit, since no one can see them anyway and they don’t affect the line of the garments.
The gömleks appear to be made with a simple cut and (usually) wide sleeves. A lightweight white fabric was used, probably cotton or linen for ease in cleaning. Gores were added to the straight-cut skirts for fullness from the hips down falling to mid-calf or ankle. Several pictures show embroidery along the seams.
The picture on the left is from Codex Vindobonensis 8626 in the Austrian National Library. The codex was painted between 1586 and 1591 by an unknown south German artist in the suite of Bartolemeo di Pezzana, ambassador of the Holy Roman Emperor Rudolph II to the Sublime Porte, the Sultan, in Istanbul. (All pictures are linked to the sites where I found them, if applicable.)
In the picture, you can see the embroidered or edged seamlines on the sleeves, the slit at the neckline which allows the underdress to be pulled over the head, and the vertical seamlines in the skirt.
The second picture on the right is actually of an extant 14th century Persian kamis, which is probably very similar in construction to an Ottoman gömlek (Persian styles heavily influenced the early Ottoman Empire).
You can see the detailed embroidery along the seamlines, as well as the straight seam construction. Curved lines were not used to fit the fabric the body, due to the wastefulness of cutting curves in valuable fabric.
Source information for this picture is available on the linked site.
For my gömlek, I used about 4 yards of white cotton batiste, cut according to the pattern shown on the left. I debated about using curved set-in sleeves, as I cannot tell from the pictures whether this is correct construction. I honestly think they probably used straight seams on the sleeves as well, but I used set-in sleeves because they are more comfortable, and because I can never get sleeves with straight seams at the shoulders to look right.
In fact, sleeves just generally give me heartburn. I tried another version before settling on this one, and they didn’t work. What confused me were the seamlines. Notice how the sleeves are seamed along the top of the shoulder and under the arm in the period pictures? Well, as everyone who has ever attempted bell sleeves knows, in order for the sleeves to hang correctly, the seam must be on the back of the shoulder, not the top. Yet these women appear to wear bell sleeves that have a seam on top of the shoulder.
So I thought, well, they must know what they’re doing. Maybe a lighter fabric hangs correctly with the seam on the shoulder. I tried it. It does NOT work. I have no idea how they managed to sew the very wide bell-style sleeves with a seam at the top, if they even did. But I did discover the wedge shape (see above sleeve pattern). When the width at the bottom is balanced on either side, it hangs very nicely even with the seam on top.
And here is my finished gömlek! Well, not quite finished, as I haven’t embroidered the seams, but that can come later. Notice how the seams on the sleeves hang, just as they appear in the first picture above.