Libertia grandiflora might be worth considering; would plant a big one so that people walk around it rather than trampling directly over it. Long term should be happy in dappled shade beneath a tree but might need watering during the first season.
"What is hateful to you, do not do to your neighbour".
Nepeta Puursian blue (horrible name!), grows to that height in semi-shade in my garden and is still semi-evergreen. It attracts bees non-stop when in flower, but might get trampled unless you can protect it with a subtle metal or cane support.
A fuchsia perhaps? Hawkshead would give you white flowers, Flashlight pale pink. Both can be kept to 40 or so cms high. And you could underplant with waldstenia ternata, one of my absolute faves. It will spread genteelly into a lovely evergreen mat that looks fab all yr and is very easy to control.
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