Based in the Netherlands, Unilever produces and markets fast-moving consumer goods, whereas Seventh Generation is a household and personal care products manufacturer and distributor.
The acquisition will help Unilever to expand its business into cleaning products.
Following the acquisition, Mattress Firm will operate as a subsidiary of Steinhoff with the existing management continuing to lead the business.
Wal-Mart Stores has announced the acquisition of Jet.com for $3.3bn. The acquisition will help Wal-Mart to expand its online presence and compete with other online retailers such as Amazon.
Wal-Mart is a multinational retail corporation based in the US, while Jet.com is an online retailer also based in the US.