This allows the seat to widen at the edges, creating more space for the users.
Both designs are supported by four wooden legs, in the form of a pair of decorative bulbous designs for the two at the front and more simple capsule shapes at the back.
The supports can be coloured to match the upholstery or left natural, with the option to have all four in the more simple versions.
The material on the sofa back and arms is tufted into triangular patterns around the rear edge of the seat.
A plain-back version of the sofa also features in the designer's pop-up shop at department store Harrods.
The designs are manufactured entirely in the UK, an important feature for the designer.
"It's been a wonderful journey to work on this collaboration with Workhouse, and be able to support authentic British craft and manufacture," said Gray, who was named Best British Designer 2013 by Elle Decoration magazine.
"The way Workhouse produces its furniture exactly resonates with my own design ethos – combining simple, elegant design with high-quality skills and craftsmanship."
The seats were presented in bright yellow and blue colours at designjunction, which took place last month during the London Design Festival.
Others products launched at the exhibition include a seat that looks like an optical illusion and a circular lightweight chair made from coloured carbon fibre.