I really like daffies, so I think you have a good daffy bed which already contains some summer and fall bloomers :))

Start with a couple aconite plants and some hellebore for really early blooms, about Feb. Buy an assortment of daffys (Check out JohnScheepers, if budget is tight wait for their November sale to buy) and you can have blooms from very early March through mid-May. You *might* be able to have tulips following - if the drainage is good and the squirrels don't see the bulbs. Then an assortment of allium will bloom in May and June. I have lilies of all sorts, which start blooming in late May and usually continue through July -- those are always finished by August, which leaves that difficult month with no perennial blooms. I've been planting snapdragons to fill in that time (I know, they aren't supposed to do well here, but I've had excellent luck with them)... those do need water but if you mulch well and then use a drip hose, about an hour of water once a week will reward you with a lot bloom even in the July-August heat.

Phlox also do very well as a filler, but also need a lot of extra water in August. Everything else I've tried seems to require more water, more often, than I'm willing to do. Some years ago I had mirabilis in a side bed which did very well without extra water, so I'm planting some seeds and will try those this year.

Good luck!