Borialis XL
Is part way to a Necky Pinta.
I’ve built a Pygmy 13, Coho and Pinguino13 and paddled the rest.
The Borealis would be perfect for him.
May not be the decks
But the thigh brace height
Google
I googled “kayak seat pad” and then selected the “Shop on Google” link and 18 choices popped up.