I have 16m2 living room, with old floor boards, which are flat. Im going to have 20mm real wood herringbone installed. The fitter came round did some checks and said he plans to fit 6mm flooring grade plywood over the old floor boards, and then glue down the wood direct to the plywood. He quoted £950, to supply the ply and fit the floor. Ive already bought the floor and adhesive. He said the ply was about £250, the rest labour. The plywood seems expensive, could he use a cheaper alternative? Is this the correct process to fit this type of floor? And is the quote fair? Im based in the North. Thanks, Jake.