As Mr Saffron says, a wireless access point would do. If you already have a router then you can probably set it up to act as a switch/access point; basically turn off its DHCP server functionality. (In fact, I'm just about to do exactly that with an old router to ensure a good signal in the garden.)
Moved (with trepidation turned relief) to BT Infinity 2 for upload speed. Happy BE user for several years.