I use a variety of year round pot plants. Have some lilies, roses, tulips, heather, daffodils. Put them on the grave when flowering, remove and keep for next year. Need to supplement from time to time, and add in plants that fail. I supplement with small flowering plants from the garden which are inexpensive but for eg putting some white cyclamens in with a pot with existing heather and trailing ivy can be nice. Its an ongoing thing, I don't know too many plants that look good all year round and all plants require maintenance in any case.