There are a lot of perennial plants that are easy to grow and come up year after year. Do you know anyone with a garden who could give you little bits of plants as most perennials can be divided up in the spring? Are there any plants swaps or amateur plant sales where you live? There are so many plants it's hard to know where to start. These are some plants I have in my garden that aren't too tall. Look them up on "Google" and see if you like any. They will be more expensive to buy per plant than annuals but they last several years and you can then divide them or take cuttings. Peonies can live 50 years!
Hardy geraniums (not the tender pelargoniums) are easy and come in several colours, veronica, catmint (nepeta), oriental poppies, hostas (like shade) campanula glomerata, hemerocallis, alchemilla mollis, geum, monarda "fireball", aster "monch", coreopsis, sidalcea, pyrethrum, aquilegia.
They won't flower all the time like annuals do, but if you have a mixture of spring, summer and autumn flowering plants there will be something out all the time.