often in the obit there is a "in lieu of flowers" notice that names a charitable organization or two that the deceased's family has chosen. I would wait for that so that you know it's going to something they would have appreciated. Then also send a nice sympathy card, and you can tell them you made a donation in your uncle's memory.
but, also, my dad got a couple of very nice potted houseplants, as well as a small "memory garden" terrarium for my mom's funeral that were sent by family/friends. He was very touched to have something like this in his home to remember Mom by. I suspect they were not nearly as expensive as a funeral flower arrangement, but perhaps similar in price to a charitable donation?? Just an idea to check into.