Ever heard of campagrain? It's a mixture of Flours: rye, barley, wheat, with some malt, and Seeds: sunflower, linseed and sesame. I add poppy seeds and oatmeal too.
The main thing is too add LOTS of seeds. A good tablespoon of each.
Mixed up the dough looks like this:
After shaping into baguettes I've taken to snipping the loaf diagonally with scissors
then pushing each section out the way in opposite directions alternately. This increases the surface area.
and adds to the crustiness.