I think hellebores are a good starting point as they flower at the most gray time of year. They bring a smile and are tough as old boots. If I was lucky they would self-seed around and spread a bit of happiness. Hellebores are definitely on the list. I would also like some snowdrops and primroses. This time of year I would want color. As the season develops then I would like some simple wild flowers preferably in some long grass, a mini-meadow would suit me just fine. I would insist on a poppy or three, but that is because even in death I will still be that predictable. (Not wishing to stretch this too far, I would be totally predictable as my ability to do much would be limited).
Have I mused too much on this? Probably, but a wander around a pretty graveyard is something I do rather enjoy. I like that they become havens for wildlife and wildflowers. I like reading the headstones and thinking about the lives that are no longer with us. I wonder about the families you see buried together and think about what their stories might have been.
and Alys's suggestion of Primula florindae is a fine one, I could almost be persuaded to be buried in such a place.