Sale of Goods legislation in this country is quite clear. What you test and try in the shop must be what you are supplied with.
If the product delivered is not what you saw and experienced in the shop, then the shop has breached the contract conditions and must either provide the goods you saw, or take them back and reimburse you.
AS the OP has posted, when she got in touch with her local Tradnig Standards Officer, he was able to direct her to template letters to send to the company that supplied the sofa.
If the sofa coccmpany does not respons , she would probably be able to take them to the Small Claims Court.