Bluebells

Vinca minor a small leafed periwinkle. there are some wonderful forms , variegated leaves, and flowers in a range of colours eg white /blue/lilac/deep purple.

There are also the lamiums, dead nettles again many variegated forms as well as flower colour white pinky purple and yellow [though yellow archangel tends to be a thug]

Then Ajuga, again leaf colour varies but most flowers are purple/blue and there is a pink form too.

I have all of the above in and around the trees in my garden.

And Cyclamen, both hederifolium and coum would thrive.

There are plenty of things you can plant to tidy it up, but none of them will stop grass or tree saplings from growing, I'm afraid. You will need to get those out yourself.

Just to add to tea drinkers suggestion...Winter aconites, crocus thommasinianus and snowdrops would look fab mixed among the later flowering bluebells and autumn flowering Cyclamen hederafolium. Maybe add some Hellibores, pulmanaria and some epimedium and you'll have a wonderful display