My bluetooth mouse and keyboard both keep disconnecting from my iMac.

I have a late-2015 iMac, and am running Mojave. The problem with Bluetooth started a month or so ago, but now it's becoming an almost daily occurrence. I have to restart the iMac to get the mouse and keyboard back up and working. This bluetooth problem started about the same time that my airport express firmware was updated. Any suggestions for a remedy would be most welcome.