You’ll find an ever increasing list of plants to grow for mulch on this page. I’ve got a lot of lawn to convert into forest and there’s soil building to do so I’m learning just like you, what to grow that can support the rest of my forest. Mulch is an important part of soil conservation, water retention and weed suppression and I’d rather grow mulch than import it.
I like comfrey. It’s one of the best biomass producers for chop and drop mulching and fertilizing. Plants grown around fruit trees support them by drawing up nutrients from deep in the soil and making it available at the surface. Comfrey can be used as mulch a few times per season and grows to about 2′ tall looking like a little shrub and attracting pollinators when flowering.