This website should help you,

http://www.thegardenhelper.com/shrubbyplants.html

I'd check with the cemetery first, they might have lists of approved plants (and another list of banned plants). It's a lovely thought to plant something as a memorial but how sad if you pick on something that isn't allowed (I'm thinking of things that could be invasive)
I always wanted to plant a rosemary on my father's grave but it's in a municipal cemetery where permanent plants aren't allowed - only flowers that will fit into the little pots in the base of the headstone.

Choisya would be a good choice

For years I have had a miniature azalea in my garden, it has purple flowers and doesn't seem to get any bigger - its only about a foot to eighteen inches tall.

Philadelphus Belle Etoile

A shrubby potentilla would flower for a long time and needs minimal maintenance.

I would go for something evergreen, so you have it looking pretty all year round. I really like tree Heather myself...erica arborea 'Estrella Gold' and 'alberts Gold' because they are at their brightest during the darkest months. They flower in spring, and don't require acid soil. They eventually reach about 1.2m. Another suggestion would be Leucothoe...which changes colour from green in summer to various shades of red in winter. It also flowers. And a dwarf form of Pieris would be nice too...Pieris japonica Variegata is extremely pretty and compact. You'd need some ericaceous compost for them though if your soil is alkaline. Hope you find something nice! :)

Lots of suggestions for you Jo - let us know what you decide on in the end!

Oh, another suggestion...drought loving Sun Roses...Cistus in all its forms is the right size, evergreen, needs no pruning and flowers beautifully in the summer for long periods!