It will depend on the terms of the trust and, possibly, state law. You may want to talk to the lawyer about charging less than his hourly rate if he is doing things like choosing investments for the trust or paying bills, as opposed to actual legal work. Good luck.
I have charged an annual fee of 1% of the value of the assets under management for serving as trustee. An hourly rate for serving as trustee might also make sense. However, you might want to consider hiring a professional care manager for day to day needs. The care manager will likely be able to provide the services you need at a much lower cost than the lawyer.
I am licensed to practice law in Pennsylvania. This communication is not intended to be legal advice and no attorney client relationship is created.