Spring flowering bulbs (tulips, crocuses, daffodils, etc.) actually require zero space in the flowerbed. They are ephemeral plants that sprout early and completely disappear from view after they bloom: not even their leaves remain. So don’t give them their own space in the garden, like you would with a perennial or shrub: that spot will just remain empty all summer. Instead, let them share space with other plants.
For example, plant your bulbs between or among other plants in your garden. Or if you divide or transplant a perennial, drop a few bulbs into the planting hole before you finish. The bulbs will emerge in the spring while the slower growing perennials and shrubs are still dormant.