Smart bulbs are meant to always have power so that the hub can interact with them and set the level. In the situation you describe you might be better off with either a smart dimmer switch and dumb bulb or a remote like a OSRAM Dimmer switch which can be installed over the dumb switch (so it always stays on) to control the smart bulb.
There are other button controllers as well some don't fit over the switch then you'd probably want a Switch Guard which is just a plastic cover to keep the switch on.
