Low growing, I take it, so as not to compete with the Hostas? Not reseeders, but spreaders like lamium or sweet woodruff may work.

tj

Celandine poppies are great reseeding natives. I'm referring to Stylophorum diphyllum, which self sows a lot where it is happy, but is not invasive. If kept watered, it won't go dormant and will rebloom, otherwise, it disappears in summer, or at least just browns out. I know there's more plants out there that fits your description, but I'm drawing a blank.

Here is a link that might be useful: link

Lungwort - May re-seed too easily