One problem with companion plant groundcovers with bulbs is the companions
will often need watering through summer when some if not most bulbs are
dormant & regular watering would cause them to rot.
I've found ornamental strawberries can get by without TOO much summer
watering, plus can bloom spring through autumn.
Campnula poscharskyana, or Serbian bellflower, also thrives with spring
moisture & summer droughtiness, & in my zone blooms for about six months
right into the heart of autumn.
Dwarf lemon thyme is a good groundcover companion for the sorts of tulips
that need it very dry in summer.
Ballotta nigra 'Variegata' is a loosely trailing groundcover; the root
remains a clump but the branchings can cover a four by four foot area, & I
have it planted with two-foot or taller tulips.
Several other herbs do well in lots of sun without need of too much
watering & remain short enough & not too densely rooted that they do well
well over bulbs. Such as Tricolor marjorum:
-paghat the ratgirl
"Of what are you afraid, my child?" inquired the kindly teacher.
"Oh, sir! The flowers, they are wild," replied the timid creature.
Click to see the full signature.