After having read about how to make a tailoring board in the "Questions" thread within the Community section, I decided to make a new sleeve board cover exactly as a work board (https://www.internationalschooloftailoring.com/community/questions/making-a-tailoring-board). I used 2 layers of thin felt, then stapled them to the underside of the sleeve board, then covered them with a layer of cotton moleksin and stapled it down. It looked messy so I lined the base with a naturally dyed and scented linen fabric to cover the staples, raw edges and wood. Next time I would just add more seam allowance and fold the fabric in neatly onto itself.

Lining window system

Original wooden sleeve board from https://www.venacavadesign.co.uk/product.php/48/0/deluxe_all_wood_sleeve_board_with_cover