Good softwood is a suitable material for rubbing strakes. It has more "give" than steel or aluminium and doesn't need painting. Scratches go unnoticed and even hefty gouges don't render them ineffective in future wall-bashing! Or use what lifeboats, pilot boats and workboats use that need rubbing strakes that take a bashing but last forever - hollow section "rubber" -though perhaps it's now some form of plastic that's used. It's costly but lasts for ever and offers plenty of cushioning.
Whatever material you choose, it's unlikely to be available off-the-shelf (apart from rubber), so perhaps a good boatyard will be able to make something specifically for your boat.
These guys seem to offer a selection of rubber ones -
. Their section DM4 seems most like the heavy duty section you see on workboats and seem a suitable size for inland waterways vessels.