I made myself a light table by getting a 24"48 piece of plixieblass from the home store and pulled the leaves out of the dining table and put a light under.
It also helps if you will put something white down first. I use a white sheet and then your white paper with black lines. This seems to make the lines easier to see on darker fabric.
I believe you were scared off by my suggestion of measuring.....just take a tape measure and guesstimate the motifs. Not exact. At least that would give you a general idea. I sometimes use the easel pads lined in 1" grids for designing. You can tape enough together. Is the design your own creation using the Welsh motifs or from a book?