...use the 2.4Ghz broadcast range as it interferes with my wireless router

Can anyone recommend one?

You have a wide choice, European DECT cordless phones use 1880 to 1900 MHz, not 2400 MHz).

USA cordless phones used to use 900 MHz, 2.4GHz and 5.8 GHz but now use 1920 to 1930 MHz.

OTOH, just as DECT base stations can interfere with reception of certain satellite TV and radio channels, you may have a proximity problem.