Euonymus fortunii, possibly Emerald 'n Gold, would give you trouble free colour all the year round, though no flowers. You could add busy lizzies or fibrous rooted begonias in summer. One of the plain blue pulmonarias would look lovely against the gold leaves at this time of year.
Lots of hardy geraniums would do well and be very low maintenance once established. They come in various heights and habits, in colours ranging from white through pink to a rather vibrant purple, and some will flower all summer. They could be underplanted with daffodils.

How about heucheras round the edge and a variegated grass called hakonechloa in the middle? Definitely low maintenance and the leaf colours would make up for the lack of flowers

I would get a shrub ,of your choice,get your garden centre recommendations and the bedding in summer is a good idea and for interest through a few hardy annual seeds in for a bit of extra colour.