I’m sorry, I can’t make a recommendation to a specific firm. To choose an arborist, check that they are certified. Here is a directory. Some are full service and can do any work required. There are also consulting arborists, who will assess the hazard a tree poses and make recommendations to you. I find checking online and with neighbors for recommendations, then confirming the certification, works well.
Here’s a brochure about tree care, and we also need to water our landscape trees. This fact sheet from the Oregon Department of Forestry, gives more advice.
I’ve hired arborists and found it reassuring to know what is happening with my big trees. I hope you find the same.