One option is on KickStarter now, allows you to add a universal remote to the side of your streamers remote…
WalMart & Amazon both have a few universal remotes that work for Roku and 1 to 6 devices. I personally liked one from Amazon called “RCRST02GR 2-Device Universal Streaming Remote” as it is VERY basic, essentially JUST adding TV control to the Roku features.
Or just search for “Roku 3 device universal” or “4 device universal” etc. For however many you want to control.
My issue with those, however, is you lose the RF / Wifi remote capabilities of the Roku which is a deal breaker for me.
I did read somewhere that one of the newer Harmony remotes does offer an RF option as well but as I am looking for SIMPLE, none of the Harmony remotes fit for me.