My TV provider doesn't have an android tv app for live tv, but does for standard android, I tried to sideload it (apk), but it's not optimized for android tv (duh), only works with mouse and kb connected. How hard is it, to edit an apk file in a way to make it usable with a remote?
Have you look into accessing the catchup or live tv through Kodi? There might already be a Kodi add-ons for your tv service.
https://www.matthuisman.nz/search/label/Add-on?m=1