In all honesty you want devices connecting into 5Ghz wherever possible as it's much much faster. Have you considered a WiFi extender?
This one will boost both the 5Ghz and 2.4Ghz signal.
By default the 5Ghz and 2.4Ghz have the same SSIDs. Devices are now becoming programmed to choose the 5Ghz signal even if the 2.4Ghz signal is stronger (which it almost always will be), iPhones (IOS11 and higher) now have a preference for 5Ghz, same for macbooks with the latest OS. My PS4 seems to choose the 5Ghz signal always too, even in poor signal.
I have split my SSID now, but just to ensure I never have to touch 2.4Ghz. For a while I had it default and most of my devices opted into 5Ghz.