The reform or rational dress movement started in the 1850s in the US, travelled to England and finally to the Continent. Its founders were women's rights activists who wanted not only economical and political freedom, but also freedom from clothes that hindered every movement. The first attempts at reformed clothing consisted of knee-length dresses worn with loose-fitting trousers, the Bloomer costume.
Trousers for women did not find any acceptance, but around the turn of the century, more and more voices rose, banishing the corset. Physicians wrote articles on the health problems such as the deformation of inner organs caused by corsets, artists claimed that a body was beautiful by nature and could only be disfigured: Venus of Milo, some said, had a waist width of 80 cm, and wasn't she beautiful? (Just to keep the overendowed among us down to earth: The Venus of Milo stands over two metres tall.)
Slowly, reformed clothing became more widely accepted. Requirements were: no corset, no hampering of any body part, light weight, weight resting on the shoulders (it was considered unhealthy to have it resting on the hips). Sadly fashion designers were obviously totally unable to imagine tasteful, elegant clothing that met these requirements. The artists were no help, either: They propagated baggy dresses. No wonder nobody wanted them at first.
While acceptance of reformed outer garments still took some time, it was quite usual by 1908 to wear only a combination of sleeveless shirt and knickers and one petticoat as undergarment. Earlier, multiple heavy petticoats had been worn as it was assumed that they warmed the body best.
Even those ladies who did not like reformed clothing began to prefer "reformed corsets" and bras to the classic corset. Reformed corsets were bodice-shaped, stiffened with cord and modeled on the natural form of the body. The cord stiffening was done similar to that of a normal corset. Bras were also more or less bodices, but with shaped breast pads, and not stiffened at all.
Both corsets and bras had to have buttons so that the other garments - petticoat, suspenders, skirts - could be attached, so the reformed variety had to have shoulder straps to take some of the weight.
basic pattern: Reformed Princess Dress, lining
Making a reformed street dress was a big deal in 1908: It must not be too conspicuously reformed. (What would people say!) House dresses were easier; even when accepting visitors a lady had more freedom at home.
Typically a suit consists of blouse, skirt and jacket. Depending on the makeup of the skirt, the blouse is worn under it and buttoned to the skirt with snaps, or over it with an elastic ribbon in the hem and a ribbon belt to cover it. In the latter case, the skirt has to have shoulder straps or be buttoned to the lining of the (loose-fitting) taille.
As for the length of the skirt, it depended on how serious the wearer was about the reform thing. The more serious wore them ankle-length without collar and unlined. The less courageous chose floor-length and even tail skirts for more formal occasions and added collars.
Although empire style was most popular for reformed dresses, they did not have to have any particular form or style. It's just that it had to fit loosely and look halfway elegant without boning and corset, and to the "corset-educated" eye only empire and princess dresses could meet both requirements.