Furnishings for dolls can be defined as miniaturized furniture. There is a distinction to be made between furniture specifically made for dolls and other types of miniature furniture which happens to fit a particular doll scale. These include salesman's samples, which are miniature versions of furniture made to show off features people could buy in full scale, and journeyman pieces, "master works," which were miniatures constructed by apprentices or journeymen as a test to show they were ready to become master carpenters or cabinet makers. Salesman's samples and master works tend to be antiques and their prices reflect their rarity.
Furniture scales vary, and it is essential to match scale to doll size if the overall effect is to be "believable." Scale is expressed as a ratio representing the proportion of the miniature as compared to full size. For example, 1:3 represents 10 cm, or 4", to every foot in the "real" world. So your SD boy, at 58 cm, corresponds to a human height of 174 cm or 5'7". His furniture should match that 1:3 scale, so an average chair that measures 18" at the seat (more important than the chair's back!) should be 6" for a 1:3 doll. Another rule of thumb for chairs, by the way, is the length from the doll's foot to his or her knee.
Furnishing can be "interior" or "exterior" and is used to create a background or scene for photoshoots. Some collectors also like to house their BJDs in miniature settings, whether on shelves, in cabinets, or in a custom made doll room. Furnishing may also include architectural features such as miniature windows and walls. Other items such as dishes, paintings, and books would be considered props rather than furniture. Props contribute to the furnishing of a scene, but props are to scenes like accessories are to dolls, although some props can be considered accessories too.
Miniature furniture has been created in a variety of materials, over a long period of time. Wood may be the most common material, ranging from Windsor chairs to upholstered dining chairs to rustic "twig" chairs, as well as various types of tables and cabinets. Metal is also common, especially for garden furniture, both in the form of bent wire and also cast iron. Plastic of various sorts and qualities has the virtue of easy molding and production. Wicker is another common material, most often seen in the form of "fan chairs." Foam covered in attractive cloth is often used for sofas and mattresses.
Miniature furniture can be found at flea markets, antique stores, and on internet marketplaces. Items such as chairs are plentiful and often inexpensive, but salesman's samples and other elaborate pieces can fetch very high prices.