Unless you’ve inherited a very old house with a very full attic, chances are you will not find really old dress patterns. women made their own, or their dressmaker kept them for them. Godey’s Lady Book was one source; and old (19th century patterns are difficult to follow, with no directions or even sizing.
Modern historic reenactors take old garments and make their own patterns, and some are available for sale online. If your goal is to find comfortable, simple clothing, you may have to choose carefully among the patterns. Soem can be maddeningly complex. If you’ve ever been involved in hsitoric societies, you also know that many people are quite fussy about the details, so don’t get caught up too much in authenticity if all you want is a wearable day dress. It’s easy to do if you get mesmerized by the explanations about horna nd wood buttons, hooks and eyes, hemming, natural fabrics and prints, and accessories.
I, for one, have no use for a reticule or a parasol tassel. My practical everyday dress is, while modest and plain, is not accurate for any historic period bu ttoday. I remind myself of that when I get fascinated by authentic Civil War era ladies’ boots or bonnets. I live today, in the 21st century, and I allow myself zippers and elastic. Elastic is an excellent thing, or our drawers would have drawstrings, and you know what can happen if the knot comes loose.
While a bit on the upper end price-wise for patterns, “The Sewing Academy” by Elizabeth Stewart Clark (http://www.elizabethstewartclark.com) has nice things for women and children. The patterns are $20 each.
James Country Mercantile (http://www.jamescountry.com) ha a wide variety of patterns for men, women and children. Some of the men’s things are military uniforms, but the shirt and pants patterns would be useful for Plain dress. There are patterns for women’s plain work dresses, and homestead dresses. Very interesting is a pattern for authentic bloomer suits, if you want something very modest for bicycle riding or beach wear. There are many patterns for hoods, caps and bonnets according to taste. Children’s clothes are well-represented.
A reenactor in Utah has a good blog on sewing historic “pioneer” style clothes, with lots of photos and advice: http://howtodresslikeapioneer.blogspot.com.
When I look at reenactment costumes, I am amused by the wide range of styles represented in any era, depending on one’s socio-economic class. Servants, slaves and homesteaders wore basic, modest dresses of wool, linen or cotton. Wealthy women, whether in a plantation setting or a city, wore elaborate costumes that required engineered underpinnings, made in fine cotton or silk. Today, there is little class distinction except in the cost of clothing. Only “Plain” says that one is simple living, rural-oriented, and unconcerned with fashion.