You could pick up a cheapo NowTV boxlet to add to your setup. Gives you iPlayer, ITV Hub, All4, Youtube, and a few other apps – no need to subscribe to NowTV
I will second Graham’s suggestion re: Chromecast. I can cast just about anything from my phone to Chromecast e.g. catchup TV, Youtube, files and media from my NAS etc. etc.
Incidentally many PC’s/laptops already have screen casting built in especially new ones running Windows 10. Many smart TV’s will have the required app without any extra hardware.