slow laggy app

You likely have network issues. Sonos can only be as good as the network it is on, since it relies on that. 

Been through support with them before and was basically told you have too many products on your network - Sky, Hive, Ring, Tapo, Alexa which is a poor excuse - cos they all work fine!!!!!

But they certainly don’t cross-talk like Sonos does!

What - Sky Q and 3 sky mini’s is less a demand on a network than 2 Play’s? 

Not familiar with Sky Qs equipment, but it is most likely. There is no need for them to constantly communicate between each other in order to maintain synchronicity in playback, like Sonos does. Sonos exercises networks in ways almost any other device doesn’t. Everyone talks about bandwidth, but Sonos does a lot more to use the network that just accept a single music stream. 

Likewise, I’m not familiar with Sky. Have you worked with Sky support? “Too many devices” seems a bit lame to me. If this is the case, the network needs to be restructured. Use Sky as a simple Internet connection for your own router. Dozens of devices is not a problem for modern networks. Hundreds of devices requires higher end equipment and may involve professional installation, depending on your capability and interests. Your profile indicates that you have a small SONOS system that shouldn’t tax your network.