We decided to come up with a cheap, home-made costume with supplies we already had around the house. It was easy to cut out felt leaves for my husband's part--a eucalyptus tree-- which he created by taping cut-out felt leaves to his brown shirt and hat using heavy-duty, double-sided picture mounting tape.
My koala costume was created by cutting out four same-size pieces of round felt and gluing two together around the edges leaving enough space to stuff some stuffing inside to make the ears stiff, and then gluing the ears to a headband. The final touch on the ears was gluing some fluff from an old costume boa. I also cut out a piece of white felt in an oval to create my white tummy, and taped it to a gray long tank top and wore darker gray leggings and light gray heels. The final touch was black toenails, some gray face paint, and black face paint around my noise in the shape of an oval.
We entered the party with me clinging to my husband-tree as shown, and our Couple Koala and Tree Costume was a hit!