In case anyone is interested, I bought these off Amazon:
CQRobot Speaker 3 Watt 4 Ohm Compatible With Arduino Motherboard, JST-PH2.0 Interface. It is Ideal for a Variety of Small Electronic Projects. https://www.amazon.co.uk/dp/B0822Z4LPH/ref=cm_sw_r_cp_api_fabc_C3VJBGDA0PTJRSKSS1W7?_encoding=UTF8&psc=1
There’s 2 speakers but only one port on the ReSpeaker so you only use one, but I can confirm it works and sounds pretty good.